CDL Glossary 2026: Every Term Explained

Commercial driving has its own vocabulary, and a lot of it isn't explained anywhere in plain language. This glossary covers every term you'll encounter getting your CDL — license classes, endorsement codes, testing terminology, medical and drug compliance terms, and the vehicle handling concepts that show up on nearly every knowledge test.

Jump to a Category

• License Classes & Permits
• Endorsement Codes
• Testing & Licensing Terms
• Medical & Drug Compliance
• Regulatory Agencies
• Vehicle & Handling Terms

License Classes & Permits

• CDL — Commercial Driver’s License: credential authorizing operation of CDL-required commercial vehicles within the license class and restrictions.
• CLP — Commercial Learner’s Permit: allows supervised practice subject to federal and state conditions; it is not an unrestricted CDL.
• Class A — generally covers qualifying heavy combinations, including a towed unit exceeding the applicable weight threshold.
• Class B — generally covers qualifying heavy single vehicles and limited lighter trailers.
• Class C — covers qualifying passenger or hazardous-material operations not meeting Class A or B weight thresholds.

Endorsement Codes

• T — Doubles/Triples trailers; N — Tank Vehicle; P — Passenger; S — School Bus.
• H — Hazardous Materials; X — Combined Tank Vehicle and Hazardous Materials.
• An endorsement adds an authorization; a restriction limits vehicles or operating conditions. The correct underlying CDL class is still required.

Testing & Licensing Terms

• ELDT — Entry-Level Driver Training: federally regulated training for covered first-time CDL/endorsement applicants.
• TPR — Training Provider Registry: FMCSA listing and reporting system for registered ELDT providers.
• SDLA — State Driver Licensing Agency: state office responsible for administering CDL/CLP credentials.
• Knowledge test — written/computer test of commercial driving rules; skills test — vehicle inspection, basic control, and road driving.
• GVWR / GCWR — manufacturer vehicle and combination weight ratings; actual weight may also matter under applicable definitions.

Medical & Drug Compliance

• DOT physical — examination for applicable commercial-driver medical qualification requirements by a certified medical examiner.
• MCSA-5875 — Medical Examination Report recording the examination; MCSA-5876 — Medical Examiner’s Certificate for a qualified driver.
• MRO — Medical Review Officer who evaluates laboratory drug-test results under DOT procedures.
• SAP — Substance Abuse Professional involved in specified return-to-duty processes.
• Clearinghouse — FMCSA database for reporting and checking covered drug-and-alcohol program violations.

Regulatory Agencies

• FMCSA — Federal Motor Carrier Safety Administration: sets federal commercial-driver licensing and motor-carrier safety rules.
• TSA — Transportation Security Administration: conducts the security threat assessment required for hazardous-materials endorsement eligibility.
• SDLA / DMV — state licensing authority: issues CLPs, CDLs, endorsements and restrictions under federal and state requirements.
• State workforce agency — administers eligibility-based training assistance programs, which are not automatic CDL grants.

Vehicle & Handling Terms

• Air-brake restriction — limits related to driving vehicles using air brakes, based on the tests and vehicle used.
• Combination vehicle — a powered unit towing one or more units.
• Off-tracking — the rear wheels follow a shorter path through a turn.
• Jackknife — an acute angle between tractor and trailer that can cause loss of control.
• Fifth wheel — connects the tractor and semitrailer.
• Kingpin — the trailer connection point.

Put These Terms Into Practice

Free CDL practice tests across the states currently available in FastLessonHub’s practice-test directory.

Sources: FMCSA; TSA; 49 CFR Parts 383, 391, 1572; state DMV/DPS/DHSMV agencies. Last verified July 2026.

Use ratings and actual weight correctly

GVWR is a vehicle manufacturer’s maximum rated loaded weight; GCWR is the manufacturer’s combined rating for vehicle and trailer. Actual gross weight is not interchangeable with a manufacturer rating. A CLP is a learner’s credential; a CDL authorizes driving within its class and endorsement/restriction limits. ELDT means entry-level driver training, not a separate license.

Free CDL study guides for the states currently available on FastLessonHub. Not affiliated with any state DMV or the FMCSA.

Understanding the three CDL classes

Class A generally covers combinations with a gross combination weight rating of at least 26,001 pounds when the towed unit has a gross vehicle weight rating above 10,000 pounds. Class B generally covers single vehicles rated at least 26,001 pounds and combinations towing no more than 10,000 pounds. Class C is for vehicles not meeting A or B thresholds but requiring a CDL based on passenger capacity or hazardous-material rules. Weight ratings and actual weight both matter under federal definitions; verify the vehicle-specific facts before choosing a class.

Permit and license terms

CLP means commercial learner’s permit. A CLP holder practices under qualifying supervision and must hold the permit at least 14 days before taking a CDL skills test. CDL means commercial driver’s license. SDLA means state driver licensing agency; it administers licensing decisions. ELDT means entry-level driver training and TPR means the FMCSA Training Provider Registry. An endorsement expands permitted activities; a restriction limits them.

Compliance and employment terms

DOT physical is a medical qualification examination by an examiner on FMCSA’s National Registry. MRO means medical review officer who evaluates laboratory drug test results. SAP means substance abuse professional involved in the return-to-duty process after specified DOT violations. Clearinghouse means the FMCSA database used for drug-and-alcohol compliance reporting and queries. A motor carrier employs or operates commercial drivers; a consortium/third-party administrator can coordinate required testing programs.

How to use this glossary

When a school advertises a quick Class A course, ask if both theory and behind-the-wheel ELDT are included, whether the training provider reports completion to the TPR, what vehicle is used for the test, and which restrictions may result. For any endorsement, find out whether the license category is sufficient, whether an additional test is needed, and whether federal or state screening applies. Read official guidance at https://www.fmcsa.dot.gov/registration/commercial-drivers-license and https://tpr.fmcsa.dot.gov .