1. Car Buying Advice
  2. /
  3. Automotive 101 Glossary

Image of a woman smiling in the driver's seat of a red car

Automotive Glossary

Enjoy a technical glossary of automotive terms,
and then use your knowledge to shop for a new car, truck, or SUV near you.


While researching your next car, you may have come across terms that are unfamiliar. Don't worry; it's not you. It's the car industry! With jargon and car-speak abound it's no wonder you might have found a few five-dollar words.

Please enjoy this AutoNation Drive glossary of automotive terms! You'll find a technical glossary and a whole bevy of terms only true car hipsters would know. You never know. It may become your next party trick.

Disclaimer: these terms may reflect the way in which AutoNation or AutoNation Drive uses them, which in some instances may differ from popular context.

Browse Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A/C compressor
The A/C compressor is the central element of the air conditioning system in a motor vehicle. It compresses the refrigerant in the refrigerant circuit of the air conditioner.

A/C drain hose
When your A/C unit converts refrigerant from a liquid to a gas, the A/C drain hose removes the water released.

Pillars are vertical supports on a vehicle. Pillars hold glass in place and add structural integrity. The A-Pillar holds the windshield in place.

Accelerator pedal linkage
The accelerator pedal linkage connects the accelerator pedal to the throttle body or carburetor throttle valve.

Acquisition fee
A fee that lending companies charge to draw the lease. Bundle acquisition fees with your monthly lease, or pay them up front. See also: bank fee.

Active pedestrian protection system
This on-board system warns drivers of impending pedestrian traffic.

Active torque transfer system (ATTS)
ATTS is a small automatic gearbox unit mated to the differential of the car. The unit sends torque to the wheel that needs power the most to optimize traction.

Actual cash value
The amount of money your car is worth, whether at buy date or sale date.

Adaptive cruise control
A cruise control system that adjusts speed to maintain a safe distance from vehicles ahead.

Adaptive headlights
This feature increases visibility around curves and hills while driving at night.

Adjustable pedals
Adjustable pedals move forward or backward to the driver. The pedals can include the brake, accelerator, and clutch pedals. This can provide an improved position with the steering wheel.

Adjustable suspension
Adjustable suspension could mean two things. Either adjusting the ride height of the car or changing the handling characteristics.

Administration fee
Fees that detail the paperwork handling at a dealership when purchasing or leasing a car.

Aerodynamic drag
Sometimes called automobile drag coefficient. Drag is a force that acts parallel and in the same direction as the airflow. The drag coefficient impacts the way the automobile passes through the surrounding air.

Aftermarket accessory
Aftermarket accessories include vehicle customization products made by third-party manufacturers.

Airbags are a safety device fitted inside a vehicle. Airbag cushions inflate in the event of a collision. Airbags keep passengers from being flung against the vehicle's structure.

Air conditioner refrigerant
Air conditioner refrigerant keeps the air coming from your air conditioning system cool. You'll find R22 in air conditioning units older than 10 years. R22 is better known as freon, and identified by the EPA as HCFC-22.

Air conditioning
Your car's air conditioning system takes the heat and moisture out of the air already in your car. What's left is cooler air.

Air filter
A device that filters incoming air fed to the engine.

Air filter restriction indicator
A device that indicates an obstruction to the air filter system.

Air filtration
The removal of dust, pollen, mold and bacteria from vehicle cabin air by a filter placed in the ventilation system.

Air pollution score
Given by the EPA, this is a score from zero to ten. Laboratory tests of new vehicles simulate the pollution in the air. The number assigned is a rating of how much pollution.

Air pump filter
A device that filters impurities from the air supply fed to the air injection system.

Airbag deactivation
A system that determines whether to activate the front passenger seat's airbag. This is based on the weight of the individual in the seat.

When a major impact occurs, a cushion deploys to reduce the passenger's chance of injury due to contact with the vehicle's interior frame, siding, and other areas.

Annual percentage rate (APR)
Annual Percentage Rate. The interest rate of credit expressed as a yearly rate.

Antenna type
In vehicle audio systems and navigation systems, types of antennas: mast, power telescoping, element and diversity.

Anti-lock brakes
A type of braking system which will automatically "pump" the brakes to prevent skidding and loss of control. Mandatory on all vehicles sold in the United States since 2013. 

Anti-lock brake system high pressure hose
In an anti-lock brake system, the reinforced hose that carries high pressure hydraulic fluid.

Anti-roll bar
A device that aids in preventing a vehicle from being stolen.

A suspension system designed to prevent the drive wheels from overly compressing during hard launched.

Can be applied to a wide variety of systems including but not limited to alarms, kill switches, and steering wheel locks, designed to make vehicles more difficult to steal. 

Anti-theft alarm
A device that uses an auditory signal to alert of a potential vehicle theft or break-in.

Anti-theft codes
A four- to six-digit numerical key necessary to return functionality to a vehicles audio head unit after it has been removed or disconnected from the battery.

Anti-theft immobilizer
An electronic device that prevents a vehicle engine from starting.

Anti-theft remote control
An electronic device that unlocks the doors of a vehicle. It may also open or shut windows, sun roof, or open the trunk.

In a turn, the part of the turn where drivers are closest to the inside of the corner. After hitting the apex, drivers are focused on exiting the corner.

Asking price
Before negotiations, the price for a vehicle asked by the dealer or other seller.

A partial zero-emission vehicle. Such vehicles may not qualify for zero-emissions standards tax credits, but has zero emissions from its fuel system and meets other emissions requirements.

Honda's Automatic Torque Transfer System, which  distributes torque output as needed between the driven axles (so that the output is most effectively used).

ATTS unit fluid
Hydraulic fluid used in Honda's Automatic Torque Transfer System.

Audio format    
Type of audio available in an audio system, such as MP3, WAV, SACD, or AAC.

Audio remote control
A device that controls a vehicle's sound system with infrared or radio waves.

Auto-delay headlights
A safety feature where headlights remain on after a vehicle is shut off to provide the occupants with light as they walk away from the vehicle.

Auto-leveling suspension
A suspension that adjusts the height of the vehicle to account for the weight of any cargo being carried. There may be settings for off-road, normal and high-speed operation.

Auto shift lock/starter safety switch
This device prevents the starter from functioning, unless the shifter is in park or neutral. It can also prevent the starter from functioning unless the brake pedal is pressed.

Automated manual transmission
A clutch-type manual transmission that employs electronic, pneumatic and/or hydraulic actuators in place of a conventional clutch pedal, and a purely mechanical shift lever. Also referred to as "DSG," "direct shift gearbox," "SMG" and "sequential manual gearbox."  Drivers may select either fully automatic shift mode or driver-controlled shift mode. Generally found on high-performance vehicles.

Automatic door unlock
A device that automatically unlocks vehicle doors after a collision.

Automatic transaxle
A combination transmission and differential/drive axle assembly.

Automatic transaxle pressure filter
The external filter on an automatic transmission.

Automatic transmission
A transmission that automatically changes gears on a vehicle. It uses a torque converter, planetary gearset, and clutches or bands to do so.

Automatic transmission bands
In an automatic transmission, these are friction-lined metal straps that are used to stop rotating clutch drums.

Automatic transmission cooler hoses
Flexible tubes that carry transmission fluid to and from a heat exchanger or oil cooler.

Automatic transmission filter
A transmission filter that prevents dirt and other particulates from getting into gears and other parts of the transmission system.

Automatic transmission fluid
In an automatic transmission, this fluid is used to lubricate and cool the transmission.

Automotive Service Excellence (ASE)
A professional certification group for automotive mechanics. To receive ASE certification, individuals have to pass exams, and demonstrate relevant work experience.

Auxiliary features
Optional parts that supplement existing systems. This may include transmission cooler, engine cooler, or a secondary gas tank. Typically available on trucks and SUVs.

Auxiliary input (Audio)
A system where an external media player can connect to an onboard entertainment system. This may be wired, through an RCA jack or USB port, or wireless, through Bluetooth or infrared.

Auxiliary lighting
Interior lamps or LED lighting positioned over specific portions of the vehicle. These usually illuminate areas such as the glove box or the footwell. They are not located in the headliner.

Awareness aids
Devices which help keep the driver of a vehicle alert and awake.

All-wheel drive. A drivetrain that employs a front, rear and center differential to provide power to all four wheels of a vehicle. See all new AWD inventory.

Axle drive fluid
The liquid used for lubricating gears inside the axle.

Axle ratio
Of the vehicle's drive axle, the number of revolutions the driveshaft makes.

Axle tramp
A form of wheel hop which is usually found in live rear axle cars. It occurs when sudden torque loads on the suspension causes the driven wheels to shake violently by slightly rotating the wheels and then springing back.

Back to top


The vertical roof support structure that is located between the front and rear doors on a typical vehicle.

A mistimed explosion in the engine cylinder or exhaust.

Backup assistance
Devices -- usually a camera -- designed to help drivers park a vehicle in reverse. See all cars, trucks, and SUVs with backup assistance.

Balance shaft belt
A cogged belt that drives a shaft to smooth out vibrations, usually in synchronization with the engine crankshaft.

Ball joints
Joints in the steering linkage and suspension system that allow a rotating movement in any direction between the joined parts.

Base price
The manufacturer's suggested retail price without any options, shipping, or dealer advertising fees. Does not include bank fees or acquisition fees.

Basic/Bumper-to-bumper warranty
Warranty type that covers everything except items subject to routine wear and tear. This also may not cover replacement items in the ordinary course of ownership -- which may include air filters, engine oil, wiper blades, and brake pads. By federal law, emissions equipment is required to be covered for two years.

Battery disconnect
A device that stops power from being transferred from the battery to the vehicle's electrical system. Can be manual or automatic. Many post-crash systems employ an automatic battery disconnect to reduce the risk of fire.  

Bed dimensions
Width, height, and depth of the pickup bed.

Bed extender
An external part that sits on top of a pickup truck's tailgate to extend the usable portion of the tailgate when hauling items that may be longer than the bed itself.

Bed features
Factory-installed, optional accessories that add functionality or longevity to a truck's bed, such as a bed extender, tonneau cover, or bed liner, that are typically available on trucks and SUVs.

Bed length 
Interior length of a cargo box or bed of the pickup.

Bed liner
Protective liner or spray-on coating on the inner surface of a truck's cargo box.

Bed type
One of the types of truck beds: long, short, flare-side, step-side, dually and flat beds. Includes beds and tanks for trucks and SUVs.

A horizontal line defined by the lower edges of the windshield, rear, and side windows and pillars.

Beverage cooler
Storage area intended to cool beverages with the help of the air conditioning system.

Bevel gears
Conical gears most often used to connect two shafts which meet at a 90-degree angle.

Bi-level purge valve
A valve that limits the flow of vapor during idling.

A plant-based diesel, often made from corn oil. Several versions are available -- some are entirely plant-based, while others contain some petro diesel.

Blind spot
An area of obstructed view in the side mirrors.

Blind spot detection
An alert system that warns the driver when another vehicle or pedestrian may be in the path of the driver's blind spot.

Block heater
An electric heater that preheats engine coolant to start a vehicle under extremely cold weather conditions.

The outer frame and panels of a vehicle.

Body water drains
Drain holes that allow for the expulsion of water from the vehicle body interior.

In a seat, these foam supports that keep the driver in an ergonomic position, and prevent sliding.

Diameter of the cylinders of an engine.

Brake bias
The percentage of braking force sent to the front and rear of a vehicle. 

Brake booster
When pressure is applied to power brakes, this device amplifies the pressure.

Brake booster bellcrank pivot
Pivot points behind some brake boosters.

Brake drying
Before a full stop is initiated, this system dries the brake pads. It uses the ABS pump to bring the brake pads close to the rotors without engaging them.

Brake fluid
The fluid used in the hydraulic brake system.

Brake lines, hoses & connections
Tubes to carry brake fluid in a brake system.

Brake linings
In a drum brake system, a heat-resistant material that is attached to the brake shoes.

Brake master cylinder
When the brake pedal is depressed, this device forces brake fluid through the brake lines.

Brake modulation
The practice of manually controlling the amount of clamping force sent to the brake caliper. Proper modulation will keep the brakes from locking. 

Brake pads
High-friction material attached to a backing plate. These contact the brake rotors to slow the vehicle.

Brake pedal
This device allows the driver to control the brakes.

Brake pedal spring
During pedal depression, the spring aids in resistance and returning the pedal to the upright position.

Braking assist
During braking, this system identifies whether a panic stop is occurring and applies additional braking force if necessary.

Branded title
Types of branding titles include rebuilt, salvage, irreparable damage, and theft recovery. A branded title indicates a vehicle is beyond repair or repair could cost more than the vehicle is worth.

Breakover angle
The maximum angle at which a vehicle can traverse a sharp ridge without making contact or hanging up between axles.

Brush guard
A metallic, tubular attachment to the front bumper of a vehicle that shields and protects the vehicle from plant life when driven off-road.

Vehicle device that protects a vehicle frame or body from collision damage.

Back to top


Support structure of the rear window on a sedan or coupe.

Cabin lighting
LEDs in the vehicle headliner that illuminate the interior space of the vehicle.

Caliper configuration
In a vehicle brake caliper, the number of hydraulic pistons and their correlation to each other.

Caliper type
Types of brake caliper: monoblock, sliding or dual sliding.

The camshaft is a shaft with a series of lobes which regulate the opening of an engine's intake and exhaust valves.

Capital reduction
The capitalized cost of a vehicle being leased in a trade-in.

Capitalized cost
Negotiated price of a vehicle being leased or traded in. One of the metrics used to determine the monthly vehicle payment.

Captive finance company
Company who finances the sale or lease of manufacturer vehicles and operates as a subsidiary of an automobile manufacturer.

Carbon dioxide
A byproduct of the combustion of fossil fuels. It consists of two oxygen atoms and one single carbon atom. One of the so-called "greenhouse gases" and naturally-occurring.

Carbon footprint
The total consumption of natural sources weighed against their global availability and sustainability.

Carbon monoxide
One of the so-called "greenhouse gases". A byproduct of the combustion of fossil fuels. It consists of one oxygen atom and single carbon atom.

In older internal combustion gasoline engines, a device mounted on the intake manifold and balances the mixture of fuel and air to the engine.

Cargo area features
Built-in amenities that serve a specific purpose in the cargo area.

Cargo door type
Types of cargo door: liftgate, vertical split-hinge or horizontal split-hinge.

Cargo hauler
Type of vehicle suited for hauling cargo. See all new cargo hauler inventory.

Cargo tie downs
Hooks, straps or eyelets that function as anchors for cargo nets and ropes used to secure objects.

Cash rebates
Purchase rebates from the manufacturer to lower the price of the vehicle. Consumers can elect cash or value as part of the vehicle down payment.

Catalytic converter
Usually situated before the muffler, the canister in the exhaust system that contains a substance that reacts chemically with the exhaust. Its purpose is to reduce harmful emissions.

Catalytic converter heat shield
A metal panel that prevents the converter heat from harming the body of the converter.

Center console trim
Aesthetic elements in the center console. May consist of wood, composite, or leather components.

Center of gravity
An object's center of mass. For a vehicle, the lower the center of gravity, the less "top-heavy" it is, and the less likely it is to roll over when it is destabilized.

Certification sales region
As certified by the EPA, a state or region where the vehicle may be sold.

Certified pre-owned vehicle
A vehicle that has been "certified" by a manufacturer-backed warranty, and may have been previously owned for a short period of time. The certification process is optional by the part of the dealer and may include inspection and service.

Charcoal canister
This device captures hydrocarbons from the fuel tank and carburetor bowl before they are expunged.

The framework or other wheeled conveyance in the undercarriage of a vehicle.

Child seat
A safety seat designed to protect small children under a certain height and weight in the event of a vehicle collision. Child safety seats provide a harness and restraints to keep the children stationery during a crash.

Child seat anchors
Hooks in the seat or other attachment locators used to attach a child safety seat into the vehicle.

Childproof safety feature(s)
Features such as window and door locks that prevent a child from injuring themselves or injury by other means.

Used on older carbureted vehicles to manually adjust the fuel-air mixture and promote easy starting.

Choke linkage
The connection between the choke switch and choke.  

City fuel economy
Miles, by number, that a car can reasonably drive within the city using one gallon of fuel. The EPA provides this number based on simulations of city driving.

Climate control
Regulation of heating and air conditioning as specified by the user. This is a computer-controlled system usually accessed from the center dash.

Climate-controlled seat filter
For air-conditioned seats, this filter removes particulates and contaminants for the air being pumped through the seat.

Climate-controlled seats
Passenger seats with heating or air conditioning features.

A salesman who improves the offer nearing the close of the sale.

Clutch bushing & linkage
In a non-hydraulic clutch system, the connection between the clutch and clutch pedal.

Clutch fluid
In a hydraulic clutch system, this fluid provides pressure to the system.

Clutch fork ball stud
In a manual transmission housing, a point which helps the clutch fork pivot.

Clutch lines & hoses
In a hydraulically actuated clutch, the tubes that carry fluid between the clutch master cylinder and the slave cylinder.

Clutch master cylinder
A cylinder that is mechanically connected to the clutch pedal. In a manual transmission, this cylinder actuates a slave cylinder and clutch fork to disengage the clutch when the pedal is depressed.

Clutch pedal
A type of vehicle insurance to cover collision damage, particularly with another vehicle involved.

Combined fuel economy
Using one gallon of fuel, this is the number of miles a vehicle is able to drive. These numbers are devised by the EPA during laboratory tests, which consist of a mixture of highway and city driving conditions.

A registration class of vehicle size between mid-size and subcompact cars. See all compact car inventory.

A display in the dashboard that shows the direction a vehicle is facing.

Comprehensive insurance
A type of vehicle insurance that covers damage beyond collision damage.

Compression ratio
Ratio of the volume of a piston when at bottom dead center to the volume of the same piston when at top dead center.

The compartment in the dashboard which provides storage, among other things.

A convertible car can be driven with the roof retracted. Sometimes called a roadster, spyder, or cabriolet.

Convertible roof type
The types of roofs available on convertible models: soft tops, hard tops, T-tops, Targa-style tops, and tops that are manual or power operated.

Convertible wind blocker
The shield on a convertible that prevents reversion of high-velocity air when passed over low-pressure, low-velocity air in the passenger area. Also known as an aeroboard.

Water and ethylene glycol mixed together. Commonly known as antifreeze, this mixture has a higher boiling point and a lower freezing point than water.

Cooled seats
Similar to heated seats, these seats utilize the interior air conditioning system to push cool air through holes in the seat. See our heated and cooled seats trim guide.

Cooling fan & shroud
A fan that moves cooling air through the radiator. The shroud creates a corridor between the radiator and the fan. When depressed, this pedal disengages the clutch from the flywheel. It is located near the floor next to the other pedals in a vehicle with a manual transmission.

Collapsible steering column
A type of vehicle insurance to cover collision damage, particularly with another vehicle involved.

Combined fuel economy
Using one gallon of fuel, this is the number of miles a vehicle is able to drive. These numbers are devised by the EPA during laboratory tests, which consist of a mixture of highway and city driving conditions.

A registration class of vehicle size between mid-size and subcompact cars.

A display in the dashboard that shows the direction a vehicle is facing.

Comprehensive insurance
A type of vehicle insurance that covers damage beyond collision damage.

Compression ratio
Ratio of the volume of a piston when at bottom dead center to the volume of the same piston when at top dead center.

The compartment in the dashboard which provides storage, among other things.

A convertible car can be driven with the roof retracted. Sometimes called a roadster, spyder, or cabriolet.

Convertible roof type
The types of roofs available on convertible models: soft tops, hard tops, T-tops, Targa-style tops, and tops that are manual or power operated.

Convertible wind blocker
The shield on a convertible that prevents reversion of high-velocity air when passed over low-pressure, low-velocity air in the passenger area. Also known as an aeroboard.

Water and ethylene glycol mixed together. Commonly known as antifreeze, this mixture has a higher boiling point and a lower freezing point than water.

Cooled seats
Similar to heated seats, these seats utilize the interior air conditioning system to push cool air through holes in the seat. See our heated and cooled seats trim guide.

Cooling fan & shroud
A fan that moves cooling air through the radiator. The shroud creates a corridor between the radiator and the fan.

A type of vehicle insurance to cover collision damage, particularly with another vehicle involved.

Combined fuel economy
Using one gallon of fuel, this is the number of miles a vehicle is able to drive. These numbers are devised by the EPA during laboratory tests, which consist of a mixture of highway and city driving conditions.

A registration class of vehicle size between mid-size and subcompact cars.

A display in the dashboard that shows the direction a vehicle is facing.

Comprehensive insurance
A type of vehicle insurance that covers damage beyond collision damage.

Compression ratio
Ratio of the volume of a piston when at bottom dead center to the volume of the same piston when at top dead center.

The compartment in the dashboard which provides storage, among other things.

A convertible car can be driven with the roof retracted. Sometimes called a roadster, spyder, or cabriolet.

Convertible roof type
The types of roofs available on convertible models: soft tops, hard tops, T-tops, Targa-style tops, and tops that are manual or power operated.

Convertible wind blocker
The shield on a convertible that prevents reversion of high-velocity air when passed over low-pressure, low-velocity air in the passenger area. Also known as an aeroboard.

Water and ethylene glycol mixed together. Commonly known as antifreeze, this mixture has a higher boiling point and a lower freezing point than water.

Cooled seats
Similar to heated seats, these seats utilize the interior air conditioning system to push cool air through holes in the seat.

Cooling fan & shroud
A fan that moves cooling air through the radiator. The shroud creates a corridor between the radiator and the fan. In the event of a front collision, the steering column collapses to avoid driver injury.

Collision insurance
A type of vehicle insurance to cover collision damage, particularly with another vehicle involved.

Combined fuel economy
Using one gallon of fuel, this is the number of miles a vehicle is able to drive. These numbers are devised by the EPA during laboratory tests, which consist of a mixture of highway and city driving conditions.

A registration class of vehicle size between mid-size and subcompact cars.

A display in the dashboard that shows the direction a vehicle is facing.

Comprehensive insurance
A type of vehicle insurance that covers damage beyond collision damage.

Compression ratio
Ratio of the volume of a piston when at bottom dead center to the volume of the same piston when at top dead center.

The compartment in the dashboard which provides storage, among other things.

A convertible car can be driven with the roof retracted. Sometimes called a roadster, spyder, or cabriolet.

Convertible roof type
The types of roofs available on convertible models: soft tops, hard tops, T-tops, Targa-style tops, and tops that are manual or power operated.

Convertible wind blocker
The shield on a convertible that prevents reversion of high-velocity air when passed over low-pressure, low-velocity air in the passenger area. Also known as an aeroboard.

Water and ethylene glycol mixed together. Commonly known as antifreeze, this mixture has a higher boiling point and a lower freezing point than water.

Cooled seats
Similar to heated seats, these seats utilize the interior air conditioning system to push cool air through holes in the seat.

Cooling fan & shroud
A fan that moves cooling air through the radiator. The shroud creates a corridor between the radiator and the fan.

Cornering brake control
To prevent oversteering, this feature on some anti-lock brake systems applies extra brake force.

Cornering lights
Located at the front corners of a vehicle, white driving lights which aid during cornering, and make the vehicle more visible to other drivers.

A type of passenger car with a sloping roof and often two doors, as opposed to four. This term was originally applied to a type of horse-drawn carriage.

Crankcase breather
A system used for releasing excessive pressure from the crankcase.

Crankcase depression regulator valve
In the crankcase, the valve regulates excessive pressure to prevent oil leakage.

Crankcase ventilation filter
Also known as the "CCV." This type of filter in the crankcase prevents foreign particulates.

Crash test ratings
In various crash tests, this rating illustrates how a vehicle performed.

Credit score
A score by which companies judge a customer's ability to pay for or complete financing on consumer goods. This is a culmination of credit reports and other personal information.

Credit tier
How a customer is rated by credit scoring bodies based on their credit reports and other personal information. There are several tiers, including platinum, gold, silver, bronze, and unclassified.

Credit union
Unlike a traditional bank, a credit union is a financial institution that is owned by its account holders.

This vehicle is a type of sports utility vehicle that features a unibody style. Similar to a standard passenger car, in that this type often presents better interior comfort and fuel economy than the SUV.

Cruise control
A system used to control the speed of the vehicle while on the highway. This allows drivers to maintain a steady speed without having to modulate the throttle.

Crumple zone
The portion of the structure of a vehicle that absorbs energy during collision impact.

Curb weight
Weight of an entire vehicle at standing without any cargo or passengers.

Curtain airbags
In the event of a side collision or rollover, these airbags are deployed to keep occupants' heads and limbs inside the vehicle.

Customer cash incentive
When a manufacturer offers cash payments to help entice the customer to purchase a vehicle.

CV joints
Constant velocity joints. These are joints that, while enabling full steering and suspension movement, cap the drive axles on both ends and send engine power. They are protected by black accordion coverings that also hold fluid.

Unlike stepped gear ratios, this transmission has a variable drive ratio. Its acceleration is steady and there are no intermittent pauses during a gear change.

In an engine, this is the chamber where gasoline is burned and turned into power. Most cars have four or six cylinders.

Cylinder configuration
The way in which cylinders are arranged in the engine.

Cylinder deactivation
In some engines, certain cylinders can be shut off to maximize fuel efficiency.

Cylinder head bolts
This bolt clamps a cylinder head to the engine block.

Back to top


In an SUV, minivan or wagon, the body frame that provides support for the roof.

The control panel that is located directly in front of the steering wheel. Often called dash or instrument panel, this displays the various controls of the vehicle.

Dead pedal
A foot rest located to the far left of the pedal box. Does not impact the operation of the vehicle.

Dealer cash incentives
When a manufacturer offers cash payments to help the dealer cover the costs of selling the vehicle. Usually paid at the time of sale.

Dealer holdback
When the vehicle is sold, the manufacturer may pay the dealer a percentage of the MSRP.

Death brake
A system designed to detect when the driver's heart stops beating.

Deceleration system
On manual shift vehicles, an emissions device that emits vacuum from the intake when the vehicle is in gear. Fuel injectors will close when decelerated and emit fewer emissions.

Declaration page
The portion of the document of insurance that states the policy holder's name, address, what is insured, and policy type.

The act of disengaging a vehicle's transmission from its driveshaft, either manually or automatically. This puts the vehicle in neutral, so while the engine may be running, the vehicle is coasting.

De Dion Suspension
A type of non-independent suspension which uses universal joints at both the differential wheels. An improvement from a live axle, thought not as sophisticated as independent suspension.   

Vehicle used for test-drive purposes by a dealership. May also refer to the test drive itself.

The loss of value incurred by a vehicle over time. This amount can be used to determine monthly payment value when leasing a vehicle.

Descent control
Using ABS and traction control systems, this off-road version of cruise control manipulates the four brakes. This allows the driver to descend down steep inclines or uneven terrain.

Destination charge
Shipping fee for delivering a vehicle from a manufacturer to a dealership. It is passed on from the dealer to the consumer, but not a factor in the MSRP of the vehicle. The destination charge is based on the vehicle itself rather than the dealership location.

An undesirable engine characteristic, when the fuel-air mixture combusts after the spark has been fired. Also referred to as "knocking," "engine knock," or "pinging".

Diesel engine
A type of engine that uses diesel fuel. In a diesel engine, the fuel air mixture is ignited primarily due to the compression in the cylinders.

Diesel engine hour meter
Over its lifetime, the amount of time a diesel engine has run. This can be a digital or analog output.

Diesel exhaust fluid (DEF)
After diesel exhaust exits the engine and before it enters a catalytic converter, this fuel is injected into the engine.

Differential fluid
Inside the differential, this fuel is used to lubricate gears.

Direct injection system
In this fuel injection system, the nozzles are located inside the combustion chamber of the system.

Direct shift gearbox
Another term for manual transmission.

Disc brake type
Rotor types in the brakes: solid, vented, slotted, cross-drilled, ceramic or carbon.

Disc changer
A dash or remote CD or DVD changer.

Displacement (CCs)
The engine cylinder volume with the piston at bottom dead center multiplied by the number of cylinders in a vehicle engine.

Disposition fee
A fee that covers the cost of retrieving and selling a leased vehicle someone chooses not to buy. This fee is passed on to the lessee.

Distributor cap
This nonconductive cap on the distributor contains the contacts leading to each individual spark plug.

Distributor rotor
The rotating component of the distributor. When aligned, it completes the circuit between the ignition and the coil.

Diverter valve
During deceleration, this valve is activated to allow air from the air pump into the intake. It then dilutes the air/fuel mixture to reduce emissions.

DMV fees
Title and license fees as required to register with a state's motor vehicle agency.

Down payment
Cash against the vehicle at the time of signing. This payment reduces the amount of the vehicle needing financing.

Dual overhead camshaft. A type of valvetrain layout where two camshafts are located within the cylinder head. One operates the intake valves while the other operates the exhaust valves.

Down payment
In the purchase of a vehicle, a cash payment that is offered by the buyer to reduce the total price of the vehicle to be financed.

Drain plug washer
On a bolt drain plug, this is a plastic or composition washer.

Drag coefficient
A numerical measurement that represents the aerodynamic resistance of a vehicle's shape. The lower the drag coefficient, the easier it is for the vehicle to move through the air.

Whether or not a vehicle is easy to drive. Automotive industry jargon that correlates to "able" and "drive".

Drive axle boots
Bendable covers that contain lubricant and cover the constant-velocity joints on a drive axle shaft.

Drive belt tensioner
On the drive belt, a device that maintains tension.

Drive belt(s)
This is a belt that transfers the rotation of the engine through the crankshaft pulley to drive various devices. These may include the alternator, water pump, air conditioning compressor, or power steering pump.

The parts of the powertrain except for the engine. After the prime mover, the portion of the vehicle that changes depending on the drive system type (front-, rear-, four-, etc.).

Drive shaft
On a rear-wheel or four-wheel drive vehicle, this sturdy metal tube connects the engine to a differential.

Drive range (EVs)
The calculated distance an electric vehicle, in particular, can travel based on fuel that remains in the tank. This is calculated by fuel level, throttle, and brake application. This range may also include other driving conditions.

Drive system
The part of the engine that creates vehicular movement. This system controls speed, torque, and direction of the engine.

The system which transfers the engine output to the vehicle's drive wheels. Included the transmission, driveshaft, and differential.

Drivetrain warranty
A warranty that specifically addresses the components of the drivetrain, including the transmission, driveshalf, and differential.  

Drivetrain mounts
Components that attach parts of a drivetrain to the chassis. This may include the transmission, transfer case, or differential housing.

Drive-off fees
Sometimes called "total due at signing". What the lessee must pay in order to drive the car from the lot. It typically includes the first month's payment and other dealership-specific administrative fees.

Driver state sensor
While a vehicle is in motion, this system detects or monitors eye movement and other vital signs of the driver.

Driving lights
Auxiliary high-beam lamps used for illuminating the roadway or other areas around the vehicle.

Drum brakes
Usually a brake in which shoes press on the inner surface of the drum. The type of brake using friction caused by a set of shoes or pads pressing outward against a cylinder-shaked part called a brake drum.

Direct shift gearbox. Also known as "automatic manual transmission".

Dual-mode hybrid
Modal hybrid vehicle with two different drive systems. The vehicle runs solely on electric motor power in the battery system in the first mode. The vehicle runs on gasoline fuel to help the electric motor recharge in the second mode.

Dusk-sensing headlights
When the light in the immediate environment dims, such as at dusk, the system turns on the headlights and taillights of the vehicle.

Dynamic brake control
A type of emergency brake assistant.

Back to top


Type of fuel that is a mixture of up to 15% ethanol and up to 85% denatured ethanol.

Early termination
When a consumer returns a leased vehicle before the original term has expired.

Easy entry
System to retract power seats or the steering column when the engine is shut off.

EGR system
In an effort to lower combustion temperature, and reduce the emission of nitrogen oxide, this device redirects exhaust to the engine intake. Short for Exhaust Gas Recirculation system.

Electric battery type
In a hybrid or electric vehicle, a type of battery that powers an electric motor. Types of batteries include: lead-acide, flooded, gel, lithium ion, absorbed glass mat, Zebra Na, NiCL2, or NiZn traction.

Electric motor performance
In terms of horsepower, torque, or kilowatts, this is the measurement of a motor's performance in an electric vehicle.

Electric motor type
In a hybrid or electric vehicle, a type of motor that powers the drive wheels. Includes a permanent magnet motor or other traction motor.

Electric vehicle
With batteries, capacitors, and one or more traction drive systems, this type of vehicle is run on electricity. See all electric vehicle inventory.

Electrochromatic rearview mirror
When detecting a glare at night, this rear view mirror system dims automatically.

Electronic brake force distribution
In some antilock braking systems, this feature applies brake force proportionally to each wheel as needed.

Electronic stability control
See stability control.

Emergency brake assist
During panic stops, this system will maximize the efficiency of the brakes.

Emergency braking preparation
A system that uses the cruise control sensors to monitor the distance of cars further down the road. A panic system in the ABS will cause the brakes to pre-fill if the gap closes rapidly.

Emergency trunk release
Inside a car's trunk, this pull-handle glows in the dark so that someone trapped inside the trunk can escape.

Chemicals in the exhaust gas that are harmful to air quality. This includes carbon monoxide, hydrocarbons, and nitrogen oxides.

Emissions certification standards
As established by the EPA and the California Air Resource Board, these numerical limits are placed on emissions and pollutants produced by a vehicle.

Emissions hoses & tubes
The hoses and tubes that are used by any emission control device.

Emissions score
Given by the EPA to new vehicles, this score gauges the total emissions produced during laboratory driving simulations of the vehicle. The score is a numerical value from 0 to 10.

Emissions standards
As regulated by the EPA, level permissions for output of chemicals such as NOx, carbon monoxide, and other vehicle pollutants.

A traditional car engine converts fuel  into motion in order to move the drivetrain of the vehicle. There are several types of car engines, including gas, diesel, hydrogen, and hybrid.

Engine auto stop/start
When a vehicle comes to a rest for a duration of time, the engine shuts off but is automatically restarted when the brake is released.

Engine control system
May refer to Engine Control Module (ECM) or Engine Control Unit (ECU). This system keeps your vehicle operating at peak performance by monitoring the sensors in the engine bay. It also manages the air-fuel mixture and regulates emission control systems.

Engine descriptor
The description of an emissions rating of an engine. This is a notation that has been attached to a vehicle engine code.

Engine displacement
Not including the volume of the combustion chambers, this is the volume of all the pistons when swept inside the cylinders of a piston engine.

Engine hour meter
The number of hours, over its lifetime, an engine has run.

Engine oil
A lubricant consisting of various base oils enhanced with various additives, especially antiwear additives, detergents, dispersants, and viscosity index improvements. Sometimes called motor oil or engine lubricant.

Engine oil level warning system
A system designed to detect when the oil of the engine is low.

Engine performance
In terms of horsepower, torque, or efficiency, the ability of an engine to perform in various conditions.

Engine size
The displacement of an engine in cubic inches or liters.

Engine thermostat
To regulate engine cooling, this device monitors the engine coolant temperature.

Entry lighting
When entering the vehicle in the dark or dark conditions, these lights provide illumination for the interior of the vehicle for the driver.

Environmental impact
For the lifespan of a vehicle, a determination of the effects the vehicle has on the environment.

EPA fuel economy/MPG estimates
As issued by the EPA, fuel economy ratings as perceived in highway or city driving conditions.

EPA interior volume
As issued by the EPA, the total cabin space within a vehicle.

EPA testing
EPA controlled driving situations in a laboratory that aid in the measurement and regulation of emissions and other vehicular pollution.

The difference between the vehicle value and what remains to be paid on a loan.

Estimated annual fuel costs
Over the course of the year, the total estimate of fueling costs. This cost estimate assumes 15,000 miles per year are driven and the price per gallon is designated by the EPA.

Ethyl alcohol, a commonly used vehicle fuel. This alcohol is also found in alcoholic beverages, but more often is a biofuel additive for gasoline.

Automotive industry shorthand for an electric vehicle.

EV effective range per charge
On a full charge, the average distance an electric vehicle can travel. This distance is measured by the EPA and posted on the vehicle's window sticker.

Evaporative control canister
This device captures hydrocarbons and fuel vapors from the fuel tank and carburetor bowl, preventing them from escaping into the air.

Evaporative control canister filter
As fuel vapors in the canister are being drawn back into the engine, this filters incoming air.

Evaporative control system
This system prevents raw fuel vapors from escaping into the atmosphere as part of emissions regulations.

Excess mileage penalty
A fee the lessee must pay when the allotted miles specified in the lease are exceeded. The fee is customarily $0.12-$0.25/mile in excess of the allotted miles.

Excess wear and tear
Beyond what would be considered average wear and tear of a vehicle in the course of its lifespan, this wear and tear exceeds insurance liability.

Exhaust gas recirculation
The EGR reduces emissions used in petrol/gasoline and diesel engines. It works by taking a portion of the exhaust gas back to the engine cylinders.

Exhaust pressure regulator valve
This valve pushes warm exhaust through the intake in an effort to aid fuel evaporation and reduce the time needed for an engine to warm up.

Exhaust manifold
An exhaust manifold pools the exhaust gases from multiple cylinders into one pipe. They may be called tubular manifolds or headers. There is usually an exhaust manifold on each cylinder.

Exhaust port
In the cylinder, this exhaust port transports spent mixture from the cylinder to the pipe. The window in the exhaust port is the opening in the cylinder bore, which is controlled by the movement of the piston.

Extended warranty
This is a type of insurance policy on your vehicle that can help assist you with expensive and unforeseen repairs.

Exterior camera
Typically for security purposes, a camera on the exterior of the motor vehicle that is used for monitoring the activity outside and around your vehicle.

Exterior mirrors adjustment type
The available control of the exterior mirrors: power, memory, or manual.

External temperature display
The temperature around your vehicle, displayed on your vehicle dash.

Back to top


Equipment installed by the manufacturer on a vehicle (as opposed to equipment that may be installed after market by the dealership or by the owner).

Factory tuner
A model of vehicle with chassis upgrades when compared to its parent model. Also called a "tuner car". This is a hobby car which is modified based upon the owner's driving style.

Automotive industry shorthand for front-engine front-wheel drive. This type of vehicle is put into motion by the front wheel system and has an engine that is located on its front axle.

Feedback fuel-air ratio control 
A system which corrects any derivation from a predetermined ideal air-fuel mixture.

The air-fuel ratio feedback control system is comprised of first means for detecting air-fuel ratio of air-fuel mixture to be inducted into the engine in accordance with a component of exhaust gas discharged from the engine.

This company, whose full name is the Full Isaac Corporation, calculates consumer credit scores.

A form of fiber-reinforced plastic using glass fiber. Nearly every vehicle on the market today has fiberglass in its parts and body.

Final-drive ratio 
The ratio of gearing between your transmission and the driven wheels. When you change your final-drive ratio, you can increase or decrease torque and change the performance metric like acceleration.

When consumers borrow money in order to purchase a vehicle.

Finance incentive
Sometimes called the "F&I office". An office within the dealership system that is responsible for contracts and other duties in relation to financing vehicle sales.

Finance rate
See "APR".

Flex-fuel engine
A type of engine that can run on more than one type of fuel.

Flex-fuel vehicle
A type of vehicle that can run on two sources at the same time through a single fuel system.

A type of short term loan used by dealerships to purchase high-cost inventory. Also called retail floor planning or inventory financing.

Fluid coupling
In vehicle transmissions, this has been used as an alternative to a mechanical clutch. It transmits rotating mechanical power through a hydrodynamic or hydrokinetic device.

In order to increase the momentum of a vehicle, this heavy wheel rotates and provides a great level of stability or reserve of available power when the power is interrupted.

Fog lights
Vehicle headlights that emit light in a bar-shaped beam. The beam is low and aimed toward the ground to illuminate the roadway in case of low visibility such as fog.

Forced induction
Using a compressor, this type of engine increases the pressure and density of the compressed air. It delivers air to the intake of an internal combustion engine.

Four-square worksheet
A negotiation technique among some car salesmen to confuse car buyers. They will mix the price of the car, down payment, trade-in value, and monthly payment onto  one sheet of paper.

Four-wheel drive
Often abbreviated as 4WD. A type of drivetrain that provides torque to all four wheels of the vehicle simultaneously, as opposed to only the front or rear. See all new 4WD inventory.

Four-wheel drift
When the rear wheels have lost traction along with the front wheels. The vehicle is sliding, as the wheels have exceeded their allowable grip.

Four-wheel steering
A drivetrain system where the driver can move the rear wheels in addition to the front wheels.

Four valves per cylinder
In an engine with four valves per cylinder, each camshaft operates two of the vales, one handles the intake, and one for the exhaust. Having four (or more) valves per cylinder offers the engine some advantages. More exhaust can be dispersed, and additional room for intake runners is allowed, among others.

Automotive industry shorthand for front-engine real-wheel drive. A type of vehicle that is moved by its rear wheels, although its engine is located ahead of the front axle.

Front brakes specifications
The width, height, and depth of all major components of the front brake rotors. This may also include the type of brake ventilation system deployed.

Front mid engine
An engine that is placed in front of the passenger cabin in a vehicle, but not on the front axle.

Front seat type
The descriptor types for the front passenger seating in a vehicle: bucket seats, sport seats, split-bench seats or captain's chairs.

Fuel capacity
The maximum volume of fuel that a fuel tank can hold.

Fuel cell vehicle
In an electric vehicle, the cell that creates electricity through a chemical process. It is done by using oxygen from the air and hydrogen.

Fuel consumption
How quickly an engine uses its fuel supply.

Fuel economy
The distance that can be traveled per the amount of fuel used. Often a descriptor when denoting the environmental impact of a vehicle.

Fuel filler cap
This cap seals the fuel filler neck on a vehicle.

Fuel filter
This is a replaceable canister that aids in the prevention of particles and other matter or contaminants from the fuel before it reaches the engine.

Fuel injection system
By directly pumping through a small nozzle under high pressure, this system disperses fuel to the engine.

Fuel lines & connections
This series of tubes and connections that enable the fuel to move from the fuel tank to the engine.

Fuel pre-filter
In diesel-fuel engines, this device filters the fuel before sending it to the fuel pump.

Fuel pump shutoff
When a motor vehicle is involved in a collision, this device shuts off the fuel pump of a vehicle to prevent possible combustion and fire.

Fuel system
The section of the car part that delivers fuel to the engine. This includes the fuel cap, tank, lines and hoses, pump, filter, injectors, and carburetor.

Fuel type
A descriptor of the type of fuel used to create power in a vehicle. Can include gasoline, ethanol, E85, diesel, bio-diesel, natural gas or electricity.

Fuel/water separator
This device removes water from the fuel alongside or as a part of the fuel filtration system.

Full-size car
A type of vehicle class from the United States and is used to describe cars that are larger than mid-size cars. This is the largest class size of vehicle and the equivalent of European categories such as executive car.

Back to top


The rate of gravitational acceleration.

Gap insurance
If the vehicle is lost, stolen, or destroyed, this insurance covers the gap between the amount the lessee's insurance company will pay to the lessee and the remaining amount the lessee owes to the leasing company or dealership.

Gas guzzler tax
When a new vehicle with poor fuel economy is purchased, this federal tax is then added onto the sale price.

Gas/electric hybrid engine
A type of powertrain that is a combination of an electric motor and gasoline or diesel engine.

Gasoline engine
The most common type of engine in a motor vehicle, which burns conventional gasoline.

See "instrumentation."

Typically the transmission in a motor vehicle -- the encasement which houses the gears.

When two or more additional gears are used to transmit power.

GPS navigation
Type of navigation system with a GPS receiver and AV components that are used by cars and handheld devices such as phones. GPS stands for "global positioning system". The system is a 24-satellite navigation system with multiple satellite signals that can find the GPS receiver's position on earth.

The section of the vehicle that is above the beltline.

Greenhouse gases
These gases are byproducts of running a motor vehicle and reduce the loss of atmospheric heat into space.

Greenhouse gas score
As designated by the EPA to each new vehicle, a score that delineates the amount of greenhouse gases emitted in driving simulations of the vehicle.

Gross vehicle weight rating
Sometimes short-handed as "GVWR." The curb weight, cargo weight capacity, and passenger weight capacity totaled together.

Ground clearance
Measurement of the distance from the lowest point of the vehicle to ground level.

Ground effect
Downforce created between airflow and a moving object.

Gyro sensor
In the navigation system, the system that senses which direction a vehicle is facing.

Back to top


Haldex clutch
In motor vehicles with all-wheel drive systems, this is a limited slip coupling that engages and disengages the secondary axel if necessary.

A type of drive axle that does half of the job when extending from a transaxle to a differential to one of the wheels. A companion shaft on the other side completes the set.

When a vehicle turns, how well a car performs in and out of the turn is referred to as "handling". Tighter speeds around corners and turns constitute better handling.

A system which allows drivers to control various vehicle functions without removing their hands from the wheel. Could include strategically placed buttons, or the use of vocal commands.  

A type of motor vehicle with a large door (instead of trunk lid) that swings upward. Often the size of a coupe or sedan, with the extra feature of the door for optimized cargo loading.

Acronym for homogeneous charge compression ignition. A type of internal combustion engine where auto-ignition takes place when gasoline and air are compressed.

Head room
How far it is between the passenger's hip and the interior rooftop of the vehicle.

Head unit
For the motor vehicle's entertainment system, the control unit.

Headlight washers
Nozzles that clean the headlights of a motor vehicle.

On the front of a vehicle, these bright lamps provide visibility of the roadway and other surrounding environs of during darkness or low visibility.

Heads-up display
A type of display that projects information onto the windshield, instead of the dashboard, to prevent driver distraction.

Heated air temperature sensor
To determine whether an engine is running hot, among other things, this sensor provides information to a computer in the motor vehicle about the air temperature coming into the engine.

Heated mirrors
Mirrors on the sides of the motor vehicle that have internal heating elements to prevent fog and other low visibility frost or particulates from forming. See all inventory with heated mirrors.

Heated windshield
A windshield with internal heating elements to prevent fogging or frosting and low visibility.

Heated windshield wiper rests
Below the wipers, a heating element that melts frozen particulates on windshield glass.

In the ventilation system, an inline fan that produces warm air by diffusing heat from the engine cooling system.

Heater hoses
The series of tubes and hoses to carry coolant between the cooling system and heater core.

A driving technique to create a smooth downshift by matching engine speed to wheel speed when driving a manual transmission.

Between the tallest part of the vehicle and level ground, a measurement of distance.

Heim joint
A type of mechanical articulating joint used anywhere an articulating joint is required. This is particularly useful when a clevis end is unsuitable for precision articulating joints.

Helical gear
On an engine, a type of cylindrical gears with a slanted tooth trace. Their contract ratio is larger than spur gears, and they are revered for their quietness and ability to transmit force.

A type of motor vehicle that is propelled by a hemispherical combustion chamber engine.

Highway fuel economy
As depicted by the EPA during simulated laboratory tests, this is the average number of miles a motor vehicle can drive on one gallon of fuel.

Hill holder
When the clutch of a motor vehicle is disengaged, this device puts additional pressure on the brakes.

Hinge type
A type of door hinge:  standard, scissor, gullwing or suicide-style.

Hip room
The distance from the drivers side lower door panel to the front passengers lower side door panel.

The term was originally coined to describe the output of steam trains as related to a draft of horses in a carriage, but today is the unit of power in a motor vehicle engine.

Heating, ventilating, and air conditioning.

Hybrid degree
A series of terms used to describe the level of hybrid technology used: full, mid, power-assist, or plug-in.

Hybrid drivetrain layout
In a hybrid vehicle, the various drivetrain layouts available: parallel, series, or combined.

Hybrid engine
A type of powertrain with a combination of electric motor and another means of movement or power generation. The most common example of a hybrid engine is gas/electric.

Hybrid gas engine performance
The ability a hybrid gas engine has in order to perform in a variety of ways. Often described in terms of horsepower or torque.

Hybrid power source
In a hybrid vehicle, the various ways an engine can receive power. May include gas/electric, plug-in, fuel cell, or pneumatic.

Hybrid vehicle
Type of vehicle that relies on a combination of internal combustion and electricity for propulsion and movement. See all hybrid vehicle inventory.

An organic compound that is made up of a single hydrogen and a single carbon atom. Most frequently used as a fuel source in motor vehicles.

Hydrogen fuel cell
A type of device that creates electricity through electrochemical reactions involving hydrogen and an oxidant.

Back to top


Idle speed
Without any extra load or accessories, the revolutions per minute of the engine when resting in normal temperature and in neutral.

Idler pulley
This pulley  tightens the slack on an engine's accessory drive belts, including those for the power steering, water pump, or air conditioning.

Ignition system
In an internal combustion engine, the system that creates the spark which then ignites the combined fuel and air mixture. This includes the battery, ignition coil, distributor, spark plugs, and all associated switches and wires.

Ignition timing
Setting when the spark in the ignition system will occur inside the combustion chamber as it relates to the piston position and angular velocity of the crankshaft.

Inherently low-emission vehicle.

Inboard brakes
This is a type of braking system that is located within the chassis, as opposed to at each wheel. 

In-car cellular phone
The ways in which to connect a mobile or cellular phone to the dashboard of a vehicle; firstly, through a handset that is built into the vehicle; secondly, a portable unit with a dock in the computer system that allows the phone or device to operate the on-board entertainment system.

Customer cash rebates or other financial offers from a manufacturer that reduces the cost of the vehicle in some way. Manufacturers produce offers in order to entice buyers to buy or lease a new vehicle.

In the passenger area of the vehicle, singular video monitors that are equipped with an entertainment system.

Independent suspension
A type of suspension which allows a single wheel to move vertically without impacting any of the other wheels.

Information pertinent to the driver of the vehicle and visible in analog or digital displays on the dashboard. Can include engine parameters, operating conditions, RPM, speed, and water temperature.

Instrumented testing
A way of researching and dissecting the performance and handling characteristics of a vehicle in a laboratory setting with measuring equipment.

Insurance Institute for Highway Safety
Often abbreviated as "IIHS". An insurance industry arm that offers guidance in order to reduce death or property damage occurring during vehicular crashes and collisions.

Intake port
This is where the intake valve sits. The intake valve opens and closes to allow air into the combustion chamber.

Integrated turn signal
Type of turn signal that can be found on or in the sideview mirror of a motor vehicle.

Intelligent alternator
During braking or coasting, this type of alternator kicks in when the engine does not require power. It remains passive if the vehicle does require power; for instance, when otherwise the  vehicle receives power from an electrical source. Found in fuel-efficient vehicles, primarily.

Intelligent car
This type of vehicle is engineered with modern telemetrics, driver awareness, and pedestrian safety technology.

On turbocharged and supercharged engines, an intercooler cools the compressed air being fed to the combustion chamber.

Interior lighting
LEDs and halogen lamps inside the vehicle to aid in illumination of the interior space.

Interior trim
The aesthetic design treatments of the interior of a motor vehicle.

Intermittent wipers
A setting on the windshield wipers that pauses the wipers for a driver-determined period of time.

Sometimes referred to as "Invoice Price." When a manufacturer sends an invoice to the dealer, this price accompanies the invoice. It is the cost of the vehicle from the factory.

Back to top


In a suspension, the vertical movement or bounce when a vehicle rides across a bump or other impediment in the road.

Jounce bumper
A jounce bumper is designed to minimize the vertical movement that occurs in the vehicle suspension when the vehicle rides across a bump or other impediment in the road.

Back to top


Keyless entry
A system that is designed to allow a driver or passenger to enter the vehicle without a key. Keyless entry systems in the US operate with a short-range transmitter to detect the key nearby. Read our Keyless Entry FAQ for more information.

Keyless ignition
Using only a push-button rather than inserting a key into the ignition slot, this system allows a driver to start the engine of a vehicle.

In an automatic transmission, this type of downshift is activated when the driver presses the accelerator pedal to the floor.

Kingpin bushings
Bearings or bushings that are used with the kingpin and steering knuckle.

Knee airbags
On the driver's side, airbas that are deployed down near the steering column and the driver's knees.

Knockdown sensor
A system that senses abnormal or otherwise unexpected pulsations that may occur during engine detonation.

Back to top


Lane departure warning system
A system that is designed to notify the driver when the motor vehicle may be veering into the next lane unexpectedly. This may also be called Lane Assist warning system. Read our Lane Assist Systems FAQ for more information.

Lane watch
Honda's proprietary system that uses video to monitor the right side blind spot during a lane change.

Lateral link
In a vehicle suspension, this link in a suspension is aligned in a way to prevent sideways motion in the wheel.

Leading link
In a vehicle suspension, this link in a suspension is aligned in a way to longitudinal motion in the wheel.

Leaf spring
Primarily used in suspensions, these are flexible pieces of steel and/or composite materials that bends when impacted by an object of force.

Lease incentive
When leasing a vehicle, this is an offer by the manufacturer to aid in the reduction of the cost of a vehicle. This may be accomplished by reducing the vehicle's interest rate or the vehicle's residual value.

Lease term
How many months the vehicle is leased from the dealership.

Leg room
How far it is from the floor of the vehicle to a person's hip, from the center line.

How far it is from the front nose of the vehicle to the most rear point of the vehicle.

A slang term for a vehicle that has not proven to be a valuable purchase, through the discovery of multiple defects that were not disclosed at the time of buying it.

The person that takes out a lease on a vehicle.

The entity that owns the vehicle that is leased.

A type of environmentally friendly vehicle known as a low emissions vehicle. This vehicle meets emissions standards as set by the LEVE program.

LEV Program
See "Low Emissions Vehicle (LEV) Program."

Automotive industry shorthand for lithium-ion batteries. This is a type of battery that performs better than many rechargeable batteries. With more power and less weight, this battery exhibits an extended driving range. The downside is that they are potentially more easily damaged by extreme temperatures.

When airflow around a moving vehicle produces vertical force.

Liftgate window
On a hatchback, wagon, or SUV, this window allows access to the cargo area without the need to fully open the back door of the vehicle.

Lift-throttle oversteer
During a hard corner, this handling causes rear tires to lose some of their grip when power is removed.

Light bar
On trucks and SUVs, this lighting is attached to the frame on the roof of a vehicle.

Limited production vehicle
Special vehicles that have exclusive detailing, trim, or performance and handling enhancements for which the manufacturer has determined only a limited number of units to be available.

Limited-slip differential
This type of differential uses a device to limit speed and torque differences between its outputs. The limited slip provides assurance that some torque is made available to both wheels, especially on slippery or wet pavement and roadways.

Limited warranty
This type of warranty is based upon the number of years or miles the vehicle is driven.

The path through a corner that best accommodates a late point to pump the brakes, a high cornering speed, and the fastest possible exit speed out of a corner.

A part in the suspension with a single joint at either end.

Lip spoiler
An aesthetic addition to the trunk lid or liftgate. This flush-mounted spoiler allows for air flow over but not under it.

Live axle
A type of axle that is responsible for transmitting power to a pair of wheels. Modern models  generally use independent suspension for improved ride quality.

A refined, liquefied natural gas. The gas is liquefied in order to remove contaminants like helium, water, or hydrocarbons. The gas is condensed into a liquid state.

Load height
A height at which an item must be raised or lifted to be loaded into the cargo area of a motor vehicle.

Lock cylinders
On a latching mechanism, the part where a key would be inserted.

Locking torque converter
When a vehicle is traveling at high speeds, and the engine is running at a low RPM, these types of torque converters will lock to a vehicle's flywheel, preventing slippage and heat generation.  

The device within a vehicle that protects the vehicle from entry without a key or the remote control if on an electronic keyless entry system.

The point at which a tire experiences skidding during braking. If a vehicle's front tires and rear tires approach lockup simultaneously, the car will be able to stop in a very short distance. Depending on the conditions of the road, load, ad tire traction, this can be very difficult. One set of wheels ordinarily will lock up before the other.

Low fuel warning indicator
To warn the driver of a low fuel supply, this LED or halogen lamp alert will flash.

Low-interest financing
A below-market interest rate loan that is offered by a captive finance company.

Propane and butane blended into one hydrocarbon gas. Sometimes referred to as GPL, LP Gas, or autogas. A small concentration of propylene and butylene may be found. Ethanethiol is added for leak detection, as it is a powerful odorant.

Luggage capacity
The cargo area or trunk space, measured in cubic feet.

Lumbar support
To aid in comfort for a driver or passenger, this device alters the shape or contour of the seat back in a motor vehicle.

Back to top


A type of gasoline or fuel that is comprised of 85% methanol and 15% gasoline. This has largely been replaced by E85, a biofuel, as M85 is more hazardous to the environment and exceptionally poisonous.

Magnetic Ride Suspension
Also known by the trade name MagneRide. A type of chassis and suspension technology from General Motors. This suspension adapts the shock absorbers to respond in altered terrain or driving conditions. It averages the optimal shock damping in order to improve driving and handling.

The manufacturer of the vehicle, e.g. Honda.

Main bearings
On an engine block, this type of bearing supports the crankshaft.

Manifold heat control valve
In order to reduce engine warm-up time, this device routes exhaust heat into the intake manifold by using a thermostat to monitor the heat levels.

Manual extending mirrors
When towing an object, these sideview mirrors can be moved further away from a motor vehicle.

Manual transmission
This type of transmission uses a clutch and shift, or gear selector in order to change gears when driving.

Manual transmission fluid
The lubricant or fluids that keep a transmission from running hot.

Manufacturers engine code
The code on an engine designated by a manufacturer to differentiate it from other engines.

Map storage
The digital space allowed for map and navigation systems in the computer system of a motor vehicle.

Marketing support
The supporting programs from a manufacturer to help boost sales and aid in dealer advertising when marketing their vehicles to consumers.

Massaging seats
A type of seat with mechanical support in the passenger and driver seats that provide lumbar and other support with passenger-controlled settings.

When maximum horsepower is reached, this is the speed of the engine.

Max Torque RPM
When maximum torque is reached, this is the speed of the engine.

Maximum cargo capacity
When the rear seats have been folded or removed, this measurement depicts the full cargo volume of a motor vehicle.

Memory settings
The system that allows a driver to create preset settings for various vehicle systems, such as power seats, mirrors, steering column positions, and others. After setting their preferred placement or functions, the driver can then recall the settings with the push of a button.

A type of vehicle in which the engine is aft of the passenger compartment, but forward of the rear axle.

Mid-size car
A type of vehicle classification in the United States that is larger than a compact car but smaller than a full-size car. Sometimes called an intermediate car. In Europe, this type of car is called a "large family car" or the D-segment category.

Mileage allowance
When a consumer has leased a vehicle, this is the number of miles they are allowed to drive without incurring an excess mileage penalty.

A type of vehicle classification in the United States that allows for passenger transport in the rear, utilizing two or three rows of seats. In Europe and the UK, this is referred to as a people mover or people carrier.

Mini/city car
A type of vehicle designed primarily for urban transportation. Significantly more compact than standard vehicle. 

The product line or brand name of the car, rather than the manufacturer. E.g., Accord.

Model year
The calendar year in which a particular product line or brand was manufactured and sold.

Money factor
An automotive industry term to express the interest rate used when calculating the monthly payment. Equal to the APR of the lease divided by 2,400. Sometimes called a "lease factor" or "lease fee".

The kind of vehicle body that uses thin, shaped joined panels to garner its strength and rigidity. As opposed to other structures which use wider panels for their frame. May be called "unit" or utilized construction.

Monroney sticker
The "window sticker" required for all new vehicles sold in the United States. This is a sticker that is attached to the side window with the following information: MSRP, engine and transmission specs, standard equipment and warranty details, optional equipment and pricing, city and highway mileage ratings as determined by the Environment Protection Agency, and crash test ratings from the National Highway Traffic Safety Administration.

Monthly payment
In a finance or lease contract, the amount of principal and interest to be paid every month.

The automotive industry abbreviation for "Miles per gallon".

The manufacturer suggested retail price.

This is a device meant to reduce the noise from the exhaust pipe of an internal combustion engine.

Multi-leaf spring
This is a type of springs where several of its leads are gathered by steel bands.

Multi-link suspension
A type of suspension with at least four links/arms, but no struts. Multi-link suspensions provide better flexibility to optimize the vehicle's ride and handling.

Back to top


National Highway Traffic Safety Administration
Often abbreviated as the "NHTSA". This agency in the United States government has the power to order manufacturers to recall or repair vehicles and equipment based on internal investigations about the safety of their products.

Natural gas engine
A type of internal combustion engine that runs on natural gas.

Navigation interface
A system which controls the navigation system of a motor vehicle. This may include a touch screen, dial, push button, or voice activation.

Navigation system
By communicating with GPS, this system can pinpoint the vehicle's location and determine a course on a map stored in the computer system.

Neutral steer
Cornering condition with the front and rear slip angles being roughly the same to aid in perfecting vehicle balance.

NHTSA campaign ID number
As assigned by the National Highway Traffic Safety Administration, this ID number is given to a recall.

NHTSA item number
As assigned by the National Highway Traffic Safety Administration, this ID number is given to a technical service bulletin.

To provide visibility to the roadway and surrounding areas in the dark, this exterior camera uses infrared technology.

NLEV program
Abbreviation for "National low emission vehicle program". Enforced by the EPA, this program encourages low emissions for light-duty vehicles and trucks. The program is opt-in by manufacturers as well as states.

The six chemical compounds that are produced in high temperature combustion. This photochemical smog contains nitrogen and oxygen atoms and is created when those chemicals interact with sunlight.

Number of speeds
How many drive ratios a transmission in a motor vehicle is capable of selecting.

NVH dampening
This system attempts to lessen noise, vibration, and harshness for the passenger compartment of a motor vehicle.

Back to top


Original equipment manufacturer. Particularly pertaining to automotive parts, this industry shorthand refers to the manufacturer of the vehicle and parts that are sent from the factory, rather than after-market parts.

Office of Defects Investigation
This NHTSA agency monitors the effectiveness of a manufacturer's recall campaign, as well as the administration and investigation of said recalls.

See also "engine oil".

Oil filter
In the lubricating system of the engine, this canister removes dirt and other abrasives from the motor oil or other lubricant.

Oil ring
Located in the ring groove closest to the crankcase, the oil ring wipes excess oil from the cylinder wall when the pistons are in motion. The oil is then drained through ring openings to the reservoir on the engine block.

Oil pump
In an internal combustion engine, the oil pump circulates the oil to the rotating bearings, pistons, and the camshaft. This keeps the bearings running smoothly and aids in the cooling of the engine.

On-board diagnosis system
The system used by the computer to identify malfunctioning components through the display of issue codes. An issue, or trouble, code will be displayed on the dash with a symbol that is lit, such as "check engine" or "service engine soon" code.

On-center feel
How responsive a steering wheel is to driving conditions when it is centered in the column. Good on-center feel occurs when the wheel has a tendency to return to the center after being deflected.

115V AC outlet
Outlet or electrical socket that receives 115v AC current from the charging system of the motor vehicle.

Optional equipment
Products that can be added to a standard edition of a vehicle to enhance various qualities, including performance and style. Optional equipment includes items such as sun roof or stereo system.

Opposite lock
Used to control a car that is oversteering and tail-fishing, this technique turns the steering wheel away from the direction the car is turning.

A type of gearset where the output shaft turns faster than the input shaft. Modern transmissions use overdrive to reduce engine RPM and improve the fuel economy.

Overhead cam
In an engine, a type of valvetrain arrangement where the camshaft is in its cylinder heads. The camshaft is placed close to the valves in order to keep the valvetrain components stiff and light. This allows the valves to open and close quickly and the engine to run at a higher RPM.

Overpressure safety switch
On a turbocharged engine, this switch warns the driver of excessive intake pressure, particularly if it may be caused by component malfunction.

A type of engine whose cylinders have greater bore diameter than stroke length. This gives a bore/stroke ratio greater than 1:1.

A handling characteristic of a vehicle that causes it to turn more sharply than the driver intends because the rear wheels are sliding to the outside of the turn.

Oxygen sensor
This sensor in the exhaust stream relays air/fuel ratio information to the control computer so that the computer can make adjustments.

Back to top


Abbreviation for "Porsche Active Aerodynamics". On 911 Turbo models, this is a combination of a multi-stage front spoiler and rear spoiler. The spoilers will extend and react in three different positions.

Panhard rod
Usually parallel to the axle, this long link provides lateral location on a rigid axle.

Parallel hybrid
A type of vehicle powered by an electric motor and internal combustion engine that are inline. This type of vehicle can be driven in either electric mode, engine mode, or combined mode. The most common type of modern hybrid vehicle.

Parking assist
This is a system that enables a vehicle to park via laser, radar, or sonar technology.

Parking lights
Sometimes referred to as "daytime running lights." These white lights increase visibility to other drivers on the road.

Parking sensors
Sensors that measure the distance to nearby cars or other objects in the drive line. These sensors alert the driver with sound or light.

PASM, or Porsche Active Suspension Management, is an electronic damping system. This system changes depending on road conditions or driving style. It varies the damping forces with the parameters of the mode chosen by the driver. It reduces pitch and roll, while wheel contact is optimized.

Passenger memory settings
These settings are stored and recalled with the touch of a button. This can include seat position, mirror adjustments, or other adjustments commonly made by drivers.

Passenger volume
The available volume of space for passengers in both the front and rear of the vehicle.

Passive safety features
Features to provide safety for passengers, the driver, and equipment that are not "active" until there is a need, for instance, in a collision. This includes seat belts, air bags, and the body construction of the vehicle.

The capacity of a motor vehicle for its occupants and cargo, in pounds. The Gross Vehicle Weight Rating (GVWR) minus its curb weight.

Payoff amount
Sometimes referred to as the "buyout amount". During a vehicle lease or loan, this is the amount required to be paid to discharge the rest of the lease.

PCV filter/PCV valve
Positive crankcase ventilation filter/positive crankcase ventilation valve. These devices aid in the venting of combustion gases into the intake system rather than into the atmosphere.

On 911 Turbo S Porsche models, this is an active anti-roll system to suppress lateral body movement during cornering. It can also aid in minimizing the lateral instability of the vehicle on an uneven roadway.

Pedal adjustment
A system that controls the position of gas, brake, and/or clutch pedals.

A type of combustion chamber that resembled a shallow peaked roof.

Pick-up truck
A light-duty truck with an enclosed cabin and open cargo area. Primarily a passenger car in the United States, they make up 18% of all total vehicles sold in North America.

Structures that support the roof, with A-pillars framing the widescreen and successive structures named for letters of the alphabet, e.g., B-pillar.

Pilot bearing
A bearing in the rear of the crankshaft to support the tip of the input shaft on the transmission.

A sliding valve snugly fitted into a cylinder that moves up and down because of pressure. In an engine, the pistons compress fluids and create fluid pressure.

The rotation of a car on a horizontal axis. This causes the nose or tail or a motor vehicle to bob up and down. E.g., dive and squat.

Planetary gears
A type of gearset that is arranged like the planets around the sun. The central gear is also called a "sun gear" and the circular grouping of gears around it are called "planet gears". The planet gears are mounted on a rotating carrier. Planetary gearsets are common in automatic transmissions.

Plenum chamber water drain valve
On some motor vehicles, this valve drains condensation from the intake plenum.

Plug-in vehicle
A type of vehicle that can be powered by electricity when plugged into a standard domestic AC power socket.

Plus size wheels
Also known as "up-sized wheels." Larger wheels than those that are included with the basic vehicle package.

Polarization coating
This coating reduces the reflected light, or glare, in side view mirrors.

Polar moment of inertia
How much an object resists rotational acceleration. If a mass of an object is distributed far from its rotational axis, the object has a higher polar moment of inertia. When it is close to the rotational axis, it has a lower polar moment of inertia.

Port fuel injection
When at least one fuel injector is mounted on the intake ports of each cylinder. Usually the injector is mounted on the intake manifold close to the port.

Post collision communication
When triggered, this system will alert authorities of a collision.

Postcrash safety
Systems and devices that aid in protecting the passenger in the aftermath of a collision.

For torque, the unit of measurement. One pound-foot equals the twisting force produced when a one-pound force is applied to the end of a one-foot-long-lever.

The rate at which work is performed. In motor vehicles, this is measured in horsepower.

Power activated release
An electronic release in the hatch or trunk of a motor vehicle.

Power band
The RPM range over which an engine gives a fraction of its peak power. The band usually extends below the torque peak of an engine to slightly above its power peak.

Power extending mirrors
A side view mirror that can move closer or farther away from the vehicle.

Power steering
Electric or hydraulic system that multiplies the force a driver exerts on the steering wheel.

Power steering fluid
The fluid used in a power steering system. This is generally red, pink, or clear.

Power steering hoses
The system of hoses and tubes used to carry fluid between the power steering system and other components of the engine.

An engine and transmission combination.

Powertrain warranty
This warranty covers the parts that make the engine move, e.g., pistons and bearings or other internal parts of the engine.

Precrash safety
Safety measures and devices that prevent a collision from occurring or lessen the chances of a driver or passenger injury in the event of a collision.

Precrash safety seats
Systems that move the passenger seats into a safe position if a precrash condition is detected.

Precrash system
Using radar or laser technology, this system detects potential collision conditions and causes other safety systems in the motor vehicle to react and deploy cautionary measures. This can include seat belts, applied brakes, etc.

Premium audio system
A name brand audio system that is provided to the vehicle manufacturer by the audio company.

Privacy glass
A tinted window that has been factory-installed. The window tint is created with a mylar covering or smoked glass and obscures the interior view of the vehicle.

Private party price
When consumers are paying for vehicles in similar private sales, this is a comparison price.

Of a tire, its aspect-ratio.

Program car
A manufacturer-owned car given to employees for company business but later purchased by a dealership. Rental cars may be delineated as "program cars," but can be verified using a VIN check through CARFAX or other services.

The unit of measurement for pressure, or pounds per square inch. Atmospheric pressure at sea level is 14.7 psi.

Abbreviation for Porsche Safety Management. A control system for stabilization when pushing the vehicle's performance limits. Especially in wet or low-grip surfaces, PSM improves traction through the brake differential and anti-slip regulation.

Purchase option
When a lessee has the right to purchase a vehicle at the end of the vehicle lease term. The purchase price will be equal to the residual value.

Purge valve
This valve vents fuel vapors from the charcoal canister to an intake, preventing the canister from being rendered nonfunctional.

Automotive industry slang for "oversteer".

A type of rod that transfers force in compression. Pushrods transfer motion from the cam followers to a more distant part of a valvetrain.

Partial zero emission vehicle. As designated by the EPA, a type of low emissions vehicle that has zero evaporative emissions.

Back to top


Rack and pinion steering
A steering mechanism that consists of a gear in mesh with a toothed bar, called a "rack." The ends of the rack are linked to the steered wheels with tie rods. When the gear is rotated by the steering shaft, it moves the rack from side to side: turning the wheels.

Radiator core & AC condenser
The radiator and air conditioning system in a motor vehicle. This system is made up of small-diameter tubes and thin, heat-conducting fins.

Radiator hoses
Tubes that are used to connect the radiator to the engine.

Radio data system
The sliver of the FM frequency that broadcasts the metadata of the files in news, traffic, and song broadcasts.

Rain-sensing wipers
Wipers that are engaged with sensors and adjust wiper speed as the rain conditions increase or decrease.

Real time traffic updates
Road sensors and communication satellites that dispense road congestion, accidents, and information.

Rear area cargo cover
A cargo cover is an opaque, additional cover or overlay that can cover or hide items in a trunk. This can be used to provide security for valuables or to shield from heat and cold.

Rear axle assembly
Axles are the units in a motor vehicle that transfer power from the transmission to the wheels. This houses the differential, shats, bearings, seals, and mounts needed to create the power transfer. There may be a need, in some vehicle types, for rear and front axles.

Rear brake type
A type of rear brake in a motor vehicle drum or disc.

Rear defroster
The system which removes frost and condensation from the rear window of a motor vehicle.

Rear door type
On a motor vehicle, the type of rear door: hinged, or sliding.

Rear electric motor performance
The ability of a rear electric motor to do work, as expressed by horsepower, torque, or kilowatts. May refer to an electric or hybrid vehicle.

Rear electric motor type
What type of an electric motor is present in a hybrid or electric motor vehicle. May refer to a permanent magnet motor or traction motor.

The system in a motor vehicle used to control the heating and cooling features; positioned behind the front row seating.

Rear seat entertainment system
The entertainment system of a motor vehicle that is visible to passengers in the rear seating area. See our guide for Best SUVs with Rear Seat Entertainment Systems.

Rear seat type
The type of seating in the rear passenger area: bench seats, bucket seats, removable seats, split-bench seats, captains chairs or convertible seats.

Rear spoiler
Airfoils attached to the trunk lid or liftgate that allow for air flow over and under it. This decreases lift and increases stability at high speeds.

Rear wheel drive
A form of engine and transmission layout in motor vehicles. The engine drives the rear wheels only. RWD was popular until the late 20th century and the most common configuration.

An incentive offered in cash by the manufacturer, which is most commonly applied to the net price of the vehicle.

The opposite of jounce, this wheel motion extends the suspension in a motor vehicle.

When a vehicle is found to exhibit a defect or safety issue, recall notices are sent to owners of vehicles by the manufacturer. Dealership service departments are responsible for replacing and repairing parts that have been recalled free of charge.

Recall notice
See "Recall".

The steering mechanism where a steering shaft turns a worm gear. This then causes a toothed metal block to move back and forth. In a recirculating track, ball bearings are placed to reduce friction between the worm gear and the block. The teeth rotate a gear connected to the steering arm, and that moves the steering linkage.

Recommended fuel type
Based on the octane rating, this fuel is what is recommended by the manufacturer of the motor vehicle.

Recommended max RPMs of an engine. A red line marked on the tachometer will indicate this on a vehicle's dashboard. There are a few variants of redlines: a colored selector as well as two lines. When the tachometer shows two lines, one indicates the sustained RPM and the other indicates the maximum RPM.

Regenerative braking
In a hybrid or electric vehicle, this assists deceleration when the motor switches from output to generator mode. This will recharge the battery as it converts a portion of the kinetic energy into electrical energy.

Remote start
An electronic fob that is used to control the ignition of the vehicle.

Remote trunk release
An electronic fob or button that controls the trunk release.

Remote window operation
An electronic fob or button that controls the window(s).

Renewable energy
Energy sources that are replenished by natural systems: solar power, wind power, hydrogen, and biofuels.

Repair kit
A set of repair equipment designed to fix issues in a flat tire. May contain emergency tire sealant and other tools necessary for that purpose.

Replacement cost
Compare "actual cash value". A way to value an insured property using the value of the current property without consideration for condition or depreciation.

Required fuel type
Based on octane rating, the recommended minimum acceptable fuel type.

Residual value
A value given to a vehicle by a leasing company based on assumptions of what it will be worth at the end of the lease. This can determine a monthly lease payment.

Retained accessory power
System in a motor vehicle that allows power accessories to remain operational after the key has been removed from the ignition.

Retractable mirrors
When parking in a compact spaces, these side view mirrors can be moved closer to the vehicle to allow for clearance.

Reverse tilt mirrors
When parallel parking, these mirrors can be tilted downward when a vehicle is in reverse.

Ride height
The distance between a point on a vehicle's body and the ground. The reference point may vary between manufacturers and automakers. The distance is often used to measure suspension deflection or the height of the body from the ground.

Ride steer
Sometimes called a "bump steer," this is an unfavorable steering technique when a wheel steers as the suspension compresses or extends.

Rigid axle
A simple type of suspension that consists of a rigid transverse member and wheel hubs that are bolted to it. It can be attached to the body by leaf springs or a mix of arms and links.

Road holding
How keen a motor vehicle is able to grip the pavement. In contrast to cornering, road holding is more commonly described as lateral acceleration and does not continue in a straight path.

Road-load horsepower
At a steady speed, the amount of power that driving wheels require to push the motor vehicle down the road. This involves many variables including speed, drag, friction, and rolling resistance.

Roadside assistance
A program which can alert a company that offers assistance when a driver or motor vehicle is stranded on the side of a road and inoperable.

How the body of a motor vehicle rotates on a longitudinal axis. May be called "sway" or "lean," although these are considered misnomers. The center of gravity for the vehicle is more likely higher than the axis around which it rotates.

Roll-over protection
Systems and devices within the motor vehicle that attempts to protect against or altogether prevent damage during rollover accidents.

Roof rack
On the roof of a motor vehicle, this plastic structure can be used to tie down or contain cargo.

Roof spoiler
Airfoils attached to the roof that allow for air flow over and under it. These are primarily attached for aesthetic purposes.

The contour of the roof on a motor vehicle.

Row count
How many rows of passenger and driver seating there are in a motor vehicle.

Revolutions per minute.

Rear-engine rear-drive. A type of motor vehicle that is propelled by the wheels at the rear and the engine is aft from the front axle.

Rubber-isolated crossmember
A structural support attached to the vehicle body with rubber isolators that absorb vibration. Engineers reduce transmission of noise and harshness to the vehicle body when they bolt suspension and driveline components laterally.

Run flat
A type of tire that can be driven temporarily even if it loses its pneumatic pressure.

Running boards
Rocker panel extensions that function as steps to aid the driver and passengers in the entering and exiting of tall vehicles.

Rust & corrosion warranty
This type of vehicle warranty covers the sheet metal on a motor vehicle that has received damage from rust or corrosion severe enough to create a hole or tear.

Back to top


SAE (Society of Automotive Engineers)
An association of professional engineers in the transportation industry. SAE sets the automotive industry standards for testing, measuring, and designing various aspects of motor vehicles.

Salvage title
A type of title for a motor vehicle where the vehicle has been damaged more than 70% of its pre-damage market value.

Satellite communication
A system that sends and receives data, crash information, concierge service and navigation for a motor vehicle using communications satellites.

Satellite radio
A type of receiver that receives radio signals that are broadcast from satellites instead of a terrestrial radio tower.

Scheduled maintenance warranty
A type of warranty that covers motor vehicle service procedures that are recommended as the cost of ownership over the lifespan of the vehicle.

Scrub radius
How far it is from where the steering axis intersects the ground to the line that moves through the center of the tire's contact patch. Sometimes called "steering offset".

Seat adjustment type
What type of adjustment control is available for the seats: manual, power, or power-with-memory.

Seat belts
The straps and harnesses on passenger seats that are designed to secure the passengers and driver during a collision.

Seat extension
This support is a metal frame covered in upholstered foam that lengthens the seat bottom in a motor vehicle.

Seat features
Design systems that allow passengers to control various aspects of the seating in a motor vehicle: temperature, adjustability, driver comfort, and others.

Seatback storage
Pockets on the back of passenger and driver seats that allow for storage of items.

Seat belt force limiters
This feature of the seat belts apply tension in order to keep the seat belt from being too tight to the point of injury to the passenger or driver.

Seating capacity
How many passengers, including the driver, can safely ride in a motor vehicle.

Secondary air supply system
An emissions-reduction system that introduces oxygen to unburnt hydrocarbons in the exhaust stream. This performs basically the same function as an air injection system but it does not rely on an air pump or diverter valve.

Security deposit
When a vehicle is being leased, this payment must be paid to the leasing company in order to hold the vehicle for the lessee.

A type of motor vehicle with four doors and a typical trunk. In the UK, a sedan may be referred to as a saloon. Technically this type of vehicle features a 3-box configuration, wherein the 3 boxes are the engine, passenger, and cargo.

Self-leveling headlights
A type of headlight system that uses the suspension height sensors to make up and down adjustments to their direction. This can provide visibility for oncoming drivers.

Self leveling suspension (SLS) filter
Sometimes referred to as an "SLS filter." A type of filter that removes contaminants and other particulates from the hydraulic fluid in a self-leveling suspension system.

Semi-eliptical leaf spring
A leaf spring attached to a vehicle body and the suspension near the middle of the spring. One of the body attachments is a shackle, which gives the spring flexibility to move up and down.

Semi-trailing arm suspension
A type of suspension system that is an independent rear-suspension. In it, each wheel hub is located by a large, triangular arm.

Separate rear audio
In some motor vehicles, a type of audio system that can deliver different audio sources to the passengers versus what is being delivered in the front of the cabin.

Sequential manual gearbox
Also referred to as "SMG," "direct shift gearbox," "DSG" and "automated manual transmission." See "Automated Manual Transmission."

Series (tire)
A tire's aspect ratio, in numerical form. A 50-series tire has an aspect ratio of 0.50.

Series hybrid
A type of electric motor vehicle that uses a gasoline engine only to recharge the batteries. The gasoline engine does not drive the wheels.

Serpentine belt
A type of drive belt that drives multiple  engine accessories, so named because it winds around multiple pulleys.

Service reminder light
When the light is on, it indicates that a vehicle is ready for some type of general vehicle maintenance.

Shields and under-hood insulation
Panels and padding that protect the under-hood components from heat.

Shift control mechanism
Where the shift control mechanism, including levers, paddles, and buttons, is located.

Shift gate
The linkage in a transmission where the motion of the gearshift lever is controlled. In some transmissions -- including Ferrari five-speeds and Mercedes-Benz automatic motor vehicles -- the shift gate is exposed around the shift lever.

Shift linkage
The mechanical collections between the operating controls and the transmission of a motor vehicle.

Shift protocol
How a driver changes gears, whether by buttons, paddles, or a lever.

Shiftable automatic transmission
A type of transmission that has a feature where the driver can actively select fully automatic or driver-controlled shift modes.

Shoulder room
How far it is from the driver's side upper door panel to the passenger's side upper door panel.

Shock absorber
This device in a motor vehicle converts motion into heat by forcing oil through tubes. This is typical for dampening suspension oscillators, and absorb suspension motion.

Side airbags
To protect the passenger's ribcage, this airbag system deploys during a side collision from the outside of a seat.

Side curtain rollover sensor
The system that, in a collision, will sense whether or not to deploy the side airbags.

Side impact beam
Beams used to protect passengers from impacts on the side of a motor vehicle.

Side pockets
Pockets on the side of passenger and driver doors that allow for storage of items.

Single-limit insurance
A type of motor vehicle insurance policy that combines a dollar limit of coverage per property damage, liability coverage, and bodily harm coverage. Similar to "split-limit insurance".

A wide region of flat pavement used in performance and handling tests. Roadholding is one such test.

Skid plate
On the bottom of a motor vehicle, this shield may be attached to guard the undercarriage when there may be a lack of ground clearance.

Sliding rear window
In the rear windshield of a truck, this small window opens and closes with a sliding maneuver on a system of metal tracks.

Automotive industry slang for an automatic transmission.

As issued by the EPA, this is a designation given to new vehicles that have a score higher in air pollution and greenhouse gas emissions that are greater than 13.

Sequential manual gearbox. Also referred to as "DSG," "direct shift gearbox" and "automated manual transmission." See "Automated Manual Transmission."

Smog-forming pollution
A smog produced by hydrocarbons and other NOx gases in the presence of sunlight.

Smoked glass
A type of vehicle window that has been darkened by pigmentation during the production process so that the interior of the vehicle has been shielded.

Snowplow prep
Hardware used to attach a removable snow plow to the front frame or bumper of a motor vehicle.

Soft-close doors
When a door is not fully latched, this type of door will slide shut automatically without slamming.

Solar power
Energy harnessed by sunlight through cells or devices to convert light energy into electricity.

Solar sunroof
A sun roof that has a solar panel embedded into the glass and can be used to power interior fans to lower cabin temperature in excessive heat conditions.

An extra wheel and tire that is often stored in the vehicle, particularly in the trunk, and can be used when one of the tires experiences a malfunction of some kind.

Spark plug wires
Cables that distribute electrical charge from ignition coils to the spark plugs.

Speaker configuration
How many and in what arrangement are the speakers in the motor vehicle's audio system. This may also include the number of channels, for instance, of a subwoofer.

Special lease
A type of lease that is sometimes called "subsidized lease" or "subvented lease". It is a lease offered by a manufacturer where the monthly payment is reduced well below what is being offered by leasing companies. The cost is absorbed by the manufacturer.

Speed-sensitive volume control
When a sound system raises or lowers the volume control based upon the speed of the vehicle.

Speed-sensitive wipers
When the speed of the windshield wipers are increased based upon the speed of the vehicle.

A type of rebate or incentive, particularly in cash, given by a dealership to encourage vehicle sales.

Split-limit insurance
A type of motor vehicle insurance policy that combines a dollar limit of coverage per property damage, liability coverage, and bodily harm coverage. The property or injury coverage may have an additional limit depending on the number of persons. Compare against "single limit insurance".

Airfoils attached to a motor vehicle for air flow over and under it. This decreases lift and increases stability at high speeds. Sometimes they are added purely for aesthetic purposes.

When the end of a motor vehicle dips while accelerating. A squat is caused by the load transfer from the front or nose of the vehicle to the rear suspension. The opposite of dive.

Stability control
Sometimes called "electronic stability control," or "ESC." This is a type of safety feature that detects skids and adjusts braking pressure to maintain the direction of the vehicle.

Stabilizer bar
Sometimes called an anti-roll or anti-sway bar. This is a device that connects the sides of a suspension in order to limit the roll in turns.

Start-stop system
In a hybrid vehicle, the system stops and then restarts the combustion engine to decrease the time it spends idling and improve fuel economy.

Starter safety switch
A type of electrical switch that prevents the vehicle starter from being engaged until certain settings and conditions are met.

Steering axis
On a steered wheel, this line intersects upper and lower steering pivots. When the motor vehicle uses strut suspension, the axis is the line through the strut mount on top and the ball joint on the bottom.

Steering column lock
A lock that keeps the steering wheel in place until the ignition switch is moved.

Steering damper
This type of damper is a shock absorber on the steering linkage that prevents "kickback" at the steering wheel. Particularly found on off-road vehicles or trucks.

Steering gearbox
A mechanism in steering to convert the motion of the steering wheel to the side-to-side motion of the lever that is connected to the linkage.

Steering geometry
A grouping of features that affect steering behavior: camber, caster, linkage arrangement, ride steer, scrub radius, toe-in, trail.

Steering intermediate shaft
This is a component of the steering system to connect the steering shaft to the steering mechanism.

Steering knuckle
Where the front wheel hubs are attached, the knuckle provides a pivoting component.

Steering linkage
The way in which rods and joints connect the steering gearbox to the wheel spindles.

Steering rack
A component in the steering to convert rotational motion of the wheel to the horizontal motion needed to operate the steering linkage.

Steering wheel adjustment
The part of the steering wheel that controls the position of the steering column as deemed necessary by the driver.

Steering wheel controls
Various controls on the steering wheel that set the entertainment, cruise control, or climate control settings. They are mounted to the steering wheel to provide distractions-free convenience.

Sticker price
See "MSRP".

Storage media
What type of physical media a sound system of a motor vehicle can play or record, including CD, DVD, hard drive, USB, or flash drive.

Straight-line tracking
How a motor vehicle can resist various irregularities in a road and run a straight line without being corrected by the driver.

How far it is between the centerline of an engine's crankshaft and the centerline of its connecting rod journal. Measured in inches.

The element of a suspension where the reinforced shock absorber is used as one of the wheel's locating members. This is usually solidly bolts the wheel hub to the bottom of the strut.

A type of motor vehicle classification that differs from a compact car by cargo space and passenger room. Subcompact cars are typically void of much of either, which was already limited to begin with in compact vehicles.

A type of loan that a borrower who has low credit may obtain to offset the risk to the lender.

Subsidized or subvented lease
See "special lease".

Super-ultra low emission vehicle. A type of vehicle that meets an emissions standard that is more strict than the ULEV.

Where the oil drains from under the crankshaft.

A portion of the roof of a vehicle that may be operable to open mechanically or physically.

A detachable or repositionable device to keep light from a vehicle's widescreen.

Sun Sensor
The sensor that measures the "sun load" to the vehicle in order to aid in adjustment of the climate control system.

A device that forces air into the internal combustion engine to increase engine power.

Supercharger drive belt
A type of belt that drives a pulley and turns the impeller of a centrifugal supercharger.

Supercharger fluid
The lubricants used in a supercharger.

The system that connects the vehicle to its wheels and creates or allows motion between the two.

Suspension fluid
The lubricants used in a suspension.

Suspension geometry
The positions of the mounting points and suspension components in relation to one another.

A type of motor vehicle classification for a vehicle with all-wheel drive that is meant for rough terrain. SUV is an abbreviation for "sport utility vehicle." See all new SUV inventory.

Back to top


This dashboard instrument displays how fast the engine is rotating, with a redline that indicates that maximum engine speed.

Tail lights
The brake lamps, reverse lights, and rear turn signal lights.

A type of motor vehicle body that has a removable roof and a roll bar behind the seats.

See "traction control."

Technical Service Bulletin
Sometimes called "secret warranties," these bulletins are issued by the manufacturer and indicate problems that affect the normal operation. They can cover known problems and will instruct the owner on how to follow through with repairs.

In contrast with recall issues, TBS repairs must first be resolved by the dealership's service department. The repairs may be subject to a fee depending on the warranty of the vehicle.

A GPS system and on-board diagnostics combined system that monitor -- and map -- a vehicle. The telematics can pinpoint exactly where a car is and how fast it is moving. The telematics system can then predict how a car is performing at the engine level.

Thermostatically controlled air cleaner
A device that helps control the temperature of an operating engine by moving different air temperatures through the exhaust manifold to the carburetor or throttle body.

The containing unit which houses a regulating valve in the intake manifold.

Throttle-body fuel injection
The type of fuel injection that is located within the throttle-body. This in turn feeds fuel to more than one cylinder at a time. This saves money by routing both fuel and air through the intake manifold.

Throttle & kick down lever ball studs
For kickdown linkages, the lubricated pivot points.

Throttle linkage
This linkage connects the accelerator pedal and the throttle body or carburetor.

Throttle system
The system that controls the amount of air that is fed to the engine.

Tie rod ends
Parts of the steering linkage that connects the wheel spindles to the pinion rack.

Tier 1 EPA Program
Originally launched in the Clean Air Act of 1994, this program by the EPA was its first generation emissions reduction program.

Tier 2 EPA Program
Originally launched in the Clean Air Act of 1994, this program by the EPA was its second generation emissions reduction program.

Timing belt
This belt dries the overhead camshaft.

Timing belt tensioner
This spring-loaded idler wheel keeps the timing belt taught enough to help the belt keep the camshaft in sync.

An adhesive film that is an overlay on vehicle windows to reduce light and, often, heat on the interior.

Tire diameter
In inches, the diameter of the tire.

Tire inflator
A product that has inflates a spare or flat tire.

Tire inflator sealant cartridge
A sealing compound that pressurizes a flat tire.

Tire load index
The numerical value that indicates a tire's capability to carry a load. This is provided by the tire manufacturer.

Tire prefix
The abbreviations assigned by tire manufacturers that indicate which types of vehicles are to go with which types of tires. E.g. "P" for passenger cars and "LT" for light trucks.

Tire pressure monitoring system
The system that monitors the amount of pressure in a tire and displays its outcome to the driver.

Tire profile
The value that indicates the relationship between a tire sidewall height and its tread width.

Tire size
The various features exhibited by a tire and displayed on the sidewall that include its prefix, profile, dimensions, capacity, and speed rating.

Tire speed rating
The value that indicates the maximum speed the tire can sustain for a ten-minute period.

Tires, all-terrain
The type of tires that can be driven on all kinds of surfaces without sacrificing traction.

Tires, heavy-duty
The type of tires that can be used on trucks or other heavy vehicles.

Tires, mud
A type of all-terrain tire that is specifically designed to be driven on mud.

Tires, truck
See "tires, heavy-duty".

Tires, off-road
See "tires, all-terrain".

Tires, winter
Snow or winter tires are a type of tire that can be used on snow and ice. Optimized particularly for winter conditions and temperatures below 7 °C (45 °F). See our best winter-ready vehicles round-up.

Sometimes referred to as the "pink slip." A document issued by the state where the vehicle has been purchased that bares ownership to the person who registered it.

Toe-control link
In a multi-link suspension, this lateral link controls the wheel's direction when the suspension moves up and down.

When opposite wheels are positioned nonparallel to each other.

Toe steer
When a wheel changes direction without being directed by a driver. Sometimes the stress of cornering, accelerating, or braking on smooth and bumpy roads can cause toe steer.

A twisting force that tends to cause rotation, particularly in the motor vehicle's engine.

Torque steer
When power is applied, a car may have a tendency to turn in a particular direction. This is common in front-drive vehicles due to reaction forces created in the half-shafts that can generate uneven steering forces in the front lines.

Total due at signing
See "drive off fees."

Tow hooks
Hooks and/or eyelets that can be attached to a vehicle frame for tow cables.

Towing capable
A type of motor vehicle that is well-suited for towing or pulling a trailer.

Towing capacity
A maximum weight, including both trailer and cargo, that the vehicle can safely carry.

How far it is from the center plane of one wheel to that on its opposite wheel.

Traction control
A system which can stop the wheels from spinning out of control when too much power is applied.

When a vehicle owner is exchanged for a new or newly purchased vehicle at a reduced price, wherein the value of the trade is equal to the price reduction.

When a driver begins to brake before entering the turn and then continues to brake as the vehicle is cornering.

Trailer hitch
A device attached to a sturdy section of the vehicle's frame to support a trailer.

Trailer hitch mountings
The attachment points that mount the trailer to the chassis.

Trailer wiring
Connectors that complete circuits for the signal and brake lights.

A type of assembly that combines the transmission and differential axle.

Transfer case fluid
Lubricant used in the transfer case.

The gearbox that provides speed and torque conversions via the rotating power source to another device. In motor vehicles, the transmission adapts the output of the internal combustion engine to the drive wheels.

Transmission modes
The settings that allow a driver to change ratios or shift points to improve fuel economy or performance.

Transmission overdrive
In an automatic transmission, the gear where the output speed is greater than its input speed. This ratio increases highway fuel economy.

Transmission, automatic
The type of motor vehicle transmission that can change gears automatically.

Transmission, manual
The type of motor vehicle transmission that requires driver input to change gears.

Transmission type
Which kind of transmission is in the motor vehicle: automatic, manual, shiftable automatic, or automated manual.

Tread squirm
The amount of flexibility in a tire thread that lies between the tread surface and the tire carcass or shell. Snow tires, for instance, have a high amount of tread squirm -- contrast with racing tires, that have no tread pattern to speak of, and very little squirm.

Trim level
A trim level, or package, is a variant of a model that is customized by several different features.

Trim, customized
A higher level of trim package that allows the buyer to customize and add features to the package. This, of course, drives up the price.

Trim, simplified
A lower level of trim package that is specified by the manufacturer. These are usually bundled by theme, for instance, technology or weather conditions.

Trip computer
An electronic device used to calculate and display trip information, such as distance traveled, average speed and fuel economy.

A type of roof on a motor vehicle that has removable panels on either side of a bar that runs the length of the A pillar to the center of its B pillar.

Tube frame
A type of vehicle body frame that consists of rigid tubes welded together.

The curvature on the side of a vehicle body.

A type of supercharger that is powered by an exhaust-driven turbine.

Turbo lag
The delay between when a vehicle's accelerator is depressed and the turbocharged engine creates a fraction of the power available at the point in the engine's power curve.

When a vehicle transitions from driving straight to driving into a corner.

Turn signals
Lights that flash in the rear headlamp area of the vehicle to tell other drivers that the driver is going to make a turn or lane change.

Turning circle
How wide a circle is (its diameter) when a vehicle makes a full 360 turn.

Two-stage unlocking
A system that requires two presses of the remote buttons in order to unlock the driver's side door.

Back to top


Used on driveshafts, these flexible joints are made up of two U-shaped yokes with a cross-shaped member shared between them.

ULEV program
A vehicle emissions standard within the LEV program that is much tighter than the LEV standard. Abbreviation for ultra-low emission vehicle standard.

Under seat storage
Beneath the seats, a console that is available to store items and valuables.

A segment of a vehicle that is not viewable from above but is exposed to the road.

Underhood label ID
This is a label that the EPA requires on all new vehicles. It is affixed to the underside of the hood and indicates the engine family for EPA testing purposes.

When a vehicle turns less sharply than a driver attempted to turn because the front wheels slide outside of the turn.

The type of company that handles insurance underwriting. See "Underwriting."

How someone to be insured is evaluated for risk, and the assessment of whether or not to offer them coverage, as well as what premium to charge.

Unitized construction
Often a monocoque construction of a vehicle body, this construction does not require a separate frame for supporting the mechanical components.

Universal joint
A type of joint that transmits rotary motion when there are two shafts that are not in a straight line. Used to accommodate a large, angular variation between the inputs and outputs. Some joints, such as the Hooke joint, will cause the output shaft to speed up and slow down twice for every revolution of the input shaft.

Universal remote control
The wireless control device that can be utilized with every portion of the entertainment system in a motor vehicle.

Universal remote transmitter
The device in a key or fob that controls the remote-operated accessories of a motor vehicle.

The covering stitched and sewn over seats, door panels, arm rests, and head rests. Usually cloth, leather, or synthetic material.

When the loan amount of a vehicle is greater than its current value. A status marker.

Back to top


Vacuum lines & hoses
The series of flexible tubes that are used to carry air, fluids, vapors and pressurized gas.

Valve clearance
How much space is allowed between a rocker arm or cam and the part it contacts to actuate a valve.

Valve float
A type of high RPM engine condition where the valve lifters release contact with the cam lobes as the springs are not strong enough to overcome the momentum of the various valvetrain components. A valve float can prevent a higher-RPM operation, and extended periods of valve float will damage the valvetrain.

Valve gear type
How many camshafts are used by an engine and the way that they are oriented in relation to the valves.

Valve lifter
Valve lifters press against the lobe in a camshaft and moves up and down as the lobe rotates.

The camshaft, drive components, and various parts that create motion in the valves.

A type of vehicle classification that allows for a greater transport opportunity of carrying people and goods. It may be bigger or smaller than a truck or SUV, but bigger than a common car.

Vanity mirrors
Mirrors placed on the back side of the sun visor, or below a flap on the sun visor, that can be used in personal grooming.

Variable gear ratio steering assembly
A type of steering mechanism that converts steering wheel rotations to side-to-side movements of a lever in the linkage.

Variable valve timing
This feature in an engine creates lift in the valvetrain so that it can be changed dynamically while it is in operation.

Vehicle Identification Number
A unique code number that identifies a vehicle. There is only one VIN per vehicle, and it is printed onto a plate or sticker affixed to the vehicle in several locations.

Vehicle type
The various classifications of motor vehicles, including large cars, midsize cars, minivans, pickup trucks, small cars, special purpose vehicles, sports utility vehicles, station wagons and vans and others.

Ventilated seats
Seats with air holes in the seat bottom that can direct cabin air.

Video game input
RCA or HDMI plugs that are located in the passenger area of the vehicle.

Video monitor
In the vehicle dashboard, headliner, or headrests, monitors that can either relay information or videos for various purposes.

Video remote control
The controls for the video system in the vehicle using the radio frequency.

Video source
The device or system that creates a video signal so that video can be fed into the entertainment system.

Viscous coupling
A particular kind of fluid coupling in which the input and output shafts mate with thin, alternately spaced discs in a cylindrical chamber. The chamber is filled with a viscous fluid that tends to cling to the discs, thereby resisting speed differences between the two shafts. Viscous couplings are used to limit the speed difference between the two outputs of a differential, or between the two axles of a car.

Back to top


Waste gate
The valve that sets limits on the boost that is produced in a turbocharger. It allows the exhaust flow to bypass the turbine section in some conditions.

Water pump
This device helps coolant circulate through the cooling system in a motor vehicle.

How power is measured in an amplifier.

Weather strip
Strips of rubber that are placed around a door or hatch.

See "environmental impact".

How far it is between the front and rear axles in a motor vehicle.

Wheel alignment
The ways in which various components may be adjusted to accommodate camber, aster, toe, and ride height.

Wheel bearings
Various assemblies that create a smooth rotation between the wheel hub and spindle.

Wheel covers
The plastic or metal covers that obscure a stamped wheel, lug nuts, and/or hubs.

Wheel cylinders, rear
These hydraulic cylinders are fitted between brake shoes that are actuated when the brakes are applied.

Wheel diameter
How wide a wheel is from edge to edge.

Wheel hop
A wheel bounce that is so violent it leaves the ground. Usually an indication that something in the suspension is wrong, and may be caused by excessive unsprung weight, lack of shock dampers, or bad axle control.

Wheel locks
Lugnuts that can prevent wheel theft due to the use of a special wrench or key.

Wheel lug nuts/bolts
Nuts that are used to attach a wheel to its hub.

Wheel offset
How far it is from the hub-mounting surface on a wheel to the centerline. Zero offset indicates the hub-mount is even with the centerline. Positive means it is toward the front/outside. Negative means it is toward the back/behind.

Wheel specs
Dimensions and details as they pertain to a wheel.

Wheel speed sensor wiring
The wiring system that dictates the speed of each wheel to a computer, which then makes adjustments to brake application in order to keep the wheels from locking up.

Wheel width
How far it is on a wheel from bead to bead.

Wholesale value
The price that a dealer purchases a vehicle from other dealers or lenders, at auction. 

Wideband oxygen sensor
An oxygen sensor that lets an engine control unit make changes to the air/fuel ratio. It has more precision than a conventional sensor.

How wide a vehicle is at its widest point.

Window control
The types of controls available on the windows: manual, power, one-touch, automatic, or remote.

Wireless data link
A way to transfer digital data, using Bluetooth or WiFi technology.

Wiring harness
The groups of wires and connectors that carry electric current through the vehicle.

Back to top


The twisting of a moving vehicle when around a vertical axis.

Back to top


Zero emission vehicle. As proposed by the EPA, this is the most restrictive vehicle emissions standard.

Zero-offset steering
In the steering geometry, this system has a scrub radius of zero. The configuration minimizes the steering effects during acceleration or braking.

Back to top