Air Brake
A braking system that uses compressed air to apply the service brakes on commercial vehicles.
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Start PracticeCDL Glossary
Clear explanations of the terminology you will encounter during CDL study, vehicle inspection and professional driving. Select any term for examples, exam context and related concepts.
Air Compressor
The engine-driven component that supplies compressed air to the brake system.
Read the complete explanation →Air Governor
A device that controls when the air compressor loads and unloads.
Read the complete explanation →Alley Dock
A backing maneuver that positions a commercial vehicle into a space approached from an angle.
Read the complete explanation →Axle Weight
The amount of vehicle weight supported by one axle or axle group.
Read the complete explanation →Backing
Moving a commercial vehicle in reverse using careful setup, mirror use and corrections.
Read the complete explanation →Blind Spot
An area around the vehicle that cannot be seen directly or through the mirrors.
Read the complete explanation →CDL
A Commercial Driver’s License required to operate specified commercial motor vehicles.
Read the complete explanation →CLP
A Commercial Learner’s Permit allowing supervised commercial-driving practice.
Read the complete explanation →Combination Vehicle
A tractor or truck connected to one or more trailers.
Read the complete explanation →Danger Zone
The area around a school bus where children may be difficult for the driver to see.
Read the complete explanation →Doubles and Triples
Combinations involving two or three trailers and requiring the appropriate endorsement.
Read the complete explanation →ELDT
Entry-Level Driver Training required for certain first-time CDL and endorsement applicants.
Read the complete explanation →Fifth Wheel
The coupling platform on a tractor that locks around the trailer kingpin.
Read the complete explanation →Gross Combination Weight Rating
The manufacturer’s maximum loaded rating for a combination of vehicles.
Read the complete explanation →Gross Vehicle Weight Rating
The manufacturer’s maximum loaded rating for a single vehicle.
Read the complete explanation →Hazard Perception
Recognizing developing road hazards early enough to respond safely.
Read the complete explanation →HazMat
Hazardous materials regulated during commercial transportation.
Read the complete explanation →Hours of Service
Federal limits and requirements governing a commercial driver’s working and driving time.
Read the complete explanation →Kingpin
The trailer pin captured by the fifth-wheel locking jaws during coupling.
Read the complete explanation →Offtracking
The tendency of rear wheels to follow a shorter path than the front wheels in a turn.
Read the complete explanation →Placard
A diamond-shaped sign identifying the hazard class of regulated cargo.
Read the complete explanation →Pre-Trip Inspection
A systematic safety inspection completed before operating a commercial vehicle.
Read the complete explanation →Rearward Amplification
The increased side-to-side movement experienced by trailers farther back in a combination.
Read the complete explanation →Space Management
Maintaining safe space around the vehicle to preserve visibility and escape options.
Read the complete explanation →Spring Brake
A mechanically applied brake held in the released position by air pressure.
Read the complete explanation →Surge
The movement of liquid cargo inside a tank as speed or direction changes.
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