Automotive Dictionary


Adaptive cruise control (ACC): An advanced cruise control system that maintains a preset distance or time interval from the vehicle ahead by automatically controlling the brakes and throttle.

Adaptive headlights: Headlights that steer in the direction the front wheels are turned to improve visibility when going around corners.

Advanced Driver Assistance Systems (ADAS): A variety of safety-related systems that monitor vehicle performance and the surrounding environment. ADAS provide a variety of driver alerts when potentially hazardous conditions exists, and some (such as automatic emergency braking) can take corrective action if the driver fails to respond appropriately to a dangerous situation.

Air filter: A paper or fabric baffle that captures dust, dirt and debris from the intake airstream to prevent it from entering the engine.

Aftermarket part: Any service replacement part not obtained from the vehicle manufacturer through a franchised dealer. Many aftermarket parts are made by the same companies that supply the original equipment part to the vehicle manufacturer.

All-wheel drive (AWD): A permanent, four-wheel drive system designed for improved traction on all surfaces and at all times. The main difference between AWD and 4WD systems is that the driver cannot disengage AWD.

Anti-freeze (coolant): The liquid in the engine cooling system that dissipates heat. Engine coolant prevents freeze-up in winter, raises the boiling point in summer, and protects the cooling system from rust and corrosion year round.

Anti-lock braking system (ABS): System that prevents wheel lock-up by automatically regulating the brakes. ABS can decrease braking distances on slippery pavement, prevent skidding and provide greater control during sudden stops.

A-Pillar: The roof support pillar at either side of the windshield.

Around view: A series of cameras that provide an overhead 360-degree view of the area immediately surrounding the vehicle via a screen on the dashboard.

Automatic emergency braking (AEB): A system that automatically applies the brakes to prevent or mitigate a collision when the car is approaching another vehicle or object at too high a rate of speed.

Autonomous vehicle (AV): A car that uses advanced technology to accelerate, brake and steer itself. There are six levels of vehicle autonomy designated by SAE Standard J3016.

Autopilot: The name Tesla uses for their semi-autonomous vehicle driving system.

Axle shaft: On front-wheel drive vehicles, the shafts that connect the transaxle to the driven wheels. Axle shafts are also used on some rear-wheel drive vehicles with independent suspensions to connect the differential assembly to the driven wheels. Axle shafts commonly have a universal joint at each end to accommodate suspension movement. In front-wheel drive applications, constant velocity joints are used that smooth power delivery and allow the wheels to be turned for steering.


Backfire: Gunshot-like sound from the engine air intake or tailpipe.

Backlash: The amount of free play between two moving parts. Commonly used in reference to the clearance between two gears that mesh with one another.

Balancing (tires): Adding small amounts of weight to a wheel to offset any imbalance present in the tire and wheel assembly. Proper balance eliminates wheel and tire vibrations that are annoying, can reduce traction in certain circumstances and cause increased tire and suspension wear.

Battery: The component that stores the electrical power needed to start the engine. The battery also powers vehicle accessories when there is insufficient power output from the charging system, and acts as a “shock absorber” for the vehicle electrical system.

Battery acid (electrolyte): The fluid in automotive batteries, a mixture of sulfuric acid and water.

Battery Electric Vehicle (BEV): A car without an internal combustion engine that is powered exclusively by electricity stored in a large onboard battery pack. Many BEVs, such as the Nissan Leaf, have a driving range of about 60-100 miles. However, the Chevrolet Bolt and all Tesla models have larger battery packs that offer driving ranges of 140 to 300+ miles.

Battery hold-down: A fastening device used to secure the battery firmly in place. The two most common types are a wedge that clamps over a protrusion near the bottom of the battery, or a bracket that fits around or across the top of the battery and is secured with long threaded rods.

Bearing: a component that reduces friction and wear between two moving parts. There are several types of bearings. Engine crankshafts generally use plain bearings, while other rotating components commonly use ball- or roller-bearings.

Biodiesel: Vegetable oil- or animal fat-based diesel fuel. Biodiesel is typically blended with petroleum-based diesel fuel in 5 or 20 percent concentrations that are commonly referred to as B5 and B20.

Blind spot monitoring: An ADAS system that monitors the driver’s blind spots at the rear quarters of the car and provides audible, visual and/or tactile alerts when a vehicle is present in them.

Bottoming: When your vehicle reaches the limits of the suspension travel (such as when going over bumps), and the vehicle’s springs are completely compressed. This results in a sudden transfer of noise/harshness, particularly through the steering, and possible contact of the vehicle undercarriage with the pavement.

B-Pillar: The roof support pillars closest to the driver’s and front-seat passenger’s heads at the rear of the front doors. “Hardtop” cars do not have B-pillars.

Brake Assist: An ADAS system that automatically applies full braking power when it detects that the driver is executing a panic stop.

Brake booster: A vacuum or hydraulic powered device that multiplies the foot pressure applied to the brake pedal to increase braking power while reducing the required driver effort.

Brake caliper: The hydraulic assembly that contains the brake pads and applies them against the brake rotor to slow or stop the car.

Brake drag: Brakes that do not completely release after application.

Brake drum: A cylindrical component that mounts on the wheel hub and has a machined inner surface that the brake shoes press against to slow or stop the vehicle.

Brake fade: A loss of braking efficiency caused by high brake temperatures. Fade typically occurs during extended and/or repeated heavy brake usage. Brake fade requires increased pedal pressure to maintain the same level of braking action. In extreme cases, the brake pedal may sink to the floor causing a near total loss of braking ability.

Brake fluid: The liquid in the brake system that acts as a hydraulic fluid. As you step on the brake pedal, brake fluid is forced through the system to apply the brake assemblies at the wheels.

Brake fluid reservoir: The container that stores a supply of brake fluid until it is needed. On most vehicles, the reservoir is mounted on the brake master cylinder.

Brake master cylinder: The brake system component that turns the mechanical power provided when you step on the brake pedal into the hydraulic power that is needed to apply the brakes and slow or stop the vehicle.

Brake rotor: A flat disc that mounts on the wheel hub and has machined outer surfaces that the brake pads press against to slow or stop the vehicle.

Brake shoes: Curved metal platforms faced with a friction material that is pressed against the inside of a brake drum to slow or stop the car. Brake shoes are applied by the wheel cylinder.

Brake pads: Metal backing plates faced with a friction material that is pressed against a brake rotor to slow or stop the car. The brake pads fit into, and are applied by, brake calipers.

Bucking: Engine miss or hesitation, or transmission slip then engagement, that causes the car to lurch repeatedly as it accelerates.

Bushing: A cylindrical metal sleeve with a hole through its center. Bushings are used to guide and support various moving parts on automobiles. Bushings are often made of bronze and, while sometimes lightly lubricated with oil or grease, depend primarily on the strength and frictional properties of the metal itself for durability.