About the CDL glossary
The CDL exam is packed with acronyms — GVWR, GCWR, CLP, CDLIS, ELD, ELDT, FMCSA — and part names that only a commercial driver ever hears: bobtail, kingpin, slack adjuster, fifth wheel, tandem, pintle hook, spring brakes. Miss one definition and a whole practice question can look like a foreign language. This glossary explains every one of them in plain English, with the exact wording you can expect to see on the FMCSA-based written test.
Every term links back into the full CDLTest360 study guides that use it in context, so a definition is never a dead end. Read a term, follow the link, and you land on the guide where that term matters — and where a practice test is waiting to prove you got it. If you're preparing for the CDL exam and there's a word in your state's manual you're not sure about, this is the fastest place to look it up.
How to use this glossary
- •Use the A–Z jump nav above to skip to a letter, or Ctrl-F (Cmd-F on Mac) to search the page for a term.
- •Click any term to see the full definition, related terms, and a link into the study guide that uses it.
- •Terms are cross-linked inside every CDLTest360 guide — anywhere a definition would help, the term is a clickable link on first mention.
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- Slack adjuster
The lever that connects the brake chamber pushrod to the S-cam and takes up slack as the brake linings wear.
- Sleeper berth
A compartment on the tractor that qualifies as rest time under FMCSA Hours of Service rules.
- Spring brakes
Fail-safe parking brakes held off by air pressure and applied by heavy springs when air pressure drops.
Glossary — frequently asked questions
- Do I need to memorize every term to pass the CDL test?
- No. You need to recognize them well enough to pick the right answer under time pressure. Focus on the acronyms in your state's CDL manual and the part names that show up in the pre-trip inspection — those are the ones tested most often.
- Where do these definitions come from?
- Every definition is written from the current FMCSA CDL Manual and, where a state rule differs, the state DMV manual. They match the wording your examiner will grade against.
- What's the difference between the glossary and the study guides?
- Glossary entries are short — a definition, related terms, a link out. The study guides go deep on a single topic with a quick-answer box, a full explanation, common mistakes, and an FAQ. Use the glossary to look something up; use the guides to actually learn it.