Trucking and Trailer Jargon: A Glossary of Terms and Nicknames

Trucking has more nicknames per part than almost any other industry — the same trailer might get called three different things depending on who's talking, and a term that means one thing to a driver can mean something else to a broker. This glossary rounds up the terms, abbreviations, and slang you're most likely to run into buying, selling, or just talking shop around trucks and trailers.

The Truck Itself: Tractor, Rig, Semi, 18-Wheeler

The vehicle that pulls a trailer goes by more names than almost anything else in the industry: tractor, truck, semi (short for semi-tractor or semi-truck), rig, big rig, and 18-wheeler are all the same thing, and which one you hear usually just comes down to regional habit or who's talking. "Power unit" is the more formal, fleet-management version of the same idea.

Within that, a day cab has no sleeping compartment and is meant for short regional runs where the driver goes home at night, while a sleeper (also called a sleeper cab, or informally a condo when it's a larger, more livable box) has a bunk built in behind the seats for over-the-road drivers who live out of the truck for days or weeks at a stretch. A conventional tractor has the engine out front under a hood, like a pickup truck; a cabover (also called COE, for cab-over-engine) sits the driver directly above the front axle with no hood at all — common in Europe and Japan and once common in the U.S. before length laws changed, but rare on American highways today outside a few specialty and vocational applications.

The Trailer: Box, Van, and a Dozen Other Names

"Trailer" itself is the generic term, but the most common type — an enclosed box with no temperature control — gets called a dry van, a box trailer, or just "the box" more or less interchangeably. Add a refrigeration unit and it becomes a reefer (from "refrigerated"), a word that's also sometimes used loosely for the refrigeration unit itself rather than the trailer as a whole.

Open-deck trailers pick up their own nicknames too: a flatbed is sometimes called a skateboard in CB slang, for its flat, wheels-under-everything profile. A step deck is also called a drop deck — same trailer, two names for the drop in deck height behind the upper deck. A lowboy is also called a lowbed, and a specific style of lowboy whose front detaches to let equipment drive straight on is a removable gooseneck, almost always shortened to RGN.

Shorter trailers pulled in pairs or groups have their own vocabulary: a pup (or pup trailer) is a short trailer, typically 26 to 29 feet, meant to run with a second one behind it — the combination is called doubles, and three in a row are triples. A turnpike double and a Rocky Mountain double both describe specific double-trailer configurations allowed on certain highways, differing mainly in the length and arrangement of the two trailers. A possum belly is a trailer — historically for hauling livestock, though the term also shows up on some drop-frame equipment trailers — with a lowered, boxed-in section between the axles for extra deck space or storage.

Read our full breakdown of flatbed, step deck, and lowboy trailers →

Hooking Up: Fifth Wheel, Kingpin, Glad Hands, and Dollies

The coupling hardware has its own set of names worth knowing. The fifth wheel is the flat, horseshoe-shaped plate mounted on the tractor's frame that the trailer locks onto; the kingpin is the pin mounted under the trailer's nose that drops into the fifth wheel and locks in place — when people say a trailer is "hooked" or "coupled," this is the connection they mean. Glad hands are the two coupling fittings (one for service air, one for emergency air) that connect the tractor's air brake lines to the trailer's, named for the way the two halves close together like a handshake when connected. The pigtail is the electrical cord that plugs the trailer's lights into the tractor.

Landing gear are the retractable legs that hold a trailer's nose up when it's disconnected from a tractor — cranked down before unhooking, cranked up before pulling out. On a set of doubles or triples, a converter dolly (or just "dolly") is the small, single-axle unit with its own fifth wheel that connects a second or third trailer to the one in front of it.

On the Road: Deadhead, Bobtail, Hot Shot, and Jake Brake

Deadhead and bobtail both describe driving without freight, but they're not the same thing: deadheading means pulling an empty trailer, while bobtailing means driving the tractor alone with no trailer attached at all. A hot shot (or hotshot) is an expedited, time-sensitive load — and by extension, "hotshot trucking" has come to describe a whole segment of the industry built around smaller trucks and trailers hauling urgent freight quickly rather than in bulk.

A Jake brake — technically an engine brake or compression release brake; "Jake" comes from Jacobs Vehicle Systems, the company that popularized it — uses the engine itself to slow the truck by releasing compressed air from the cylinders, producing the distinctive rattling sound you hear from a truck braking down a grade, and the reason so many "no engine braking" signs exist near residential areas. A headache rack is the metal frame mounted behind a truck's cab, originally meant to keep a shifting load from crushing the cab in a hard stop, and now also a common mounting point for lights and antennas. An APU (auxiliary power unit) is a small onboard generator that lets a driver run climate control and electronics in the sleeper without idling the main engine; a PTO (power take-off) draws mechanical power directly off the truck's engine or transmission to run separate equipment, like a dump trailer's hydraulics.

The Business Side: FTL, LTL, Detention, and Who's Who

FTL (full truckload) means one shipment fills an entire trailer for one customer start to finish; LTL (less-than-truckload) means a trailer carries multiple smaller shipments from different customers, consolidated and later broken apart at a terminal. Drayage refers specifically to short hauls of containerized freight, typically moving a container between a port or rail yard and a nearby warehouse.

Detention is the time — and often the fee — that accrues when a driver is held at a shipper or receiver beyond the agreed-upon free time to load or unload; demurrage is a related but distinct charge for a container or trailer sitting too long at a port, rail yard, or terminal rather than at a dock. A layover is downtime a driver is paid for while waiting on the next available load, usually when a delay isn't the carrier's fault. A lumper is a third-party worker hired to load or unload freight at a dock, paid separately from the freight charge itself, usually because the shipper or receiver doesn't have its own dock labor available.

On the people side: an owner-operator owns (or is buying) the truck they drive and either hauls under their own operating authority or leases onto a carrier; a company driver drives a truck the carrier owns, on the carrier's payroll; a lease-operator sits in between, leasing a truck from a company — often the same one they drive for — rather than owning it outright. A broker arranges freight between a shipper and a carrier without hauling it themselves, while a dispatcher manages a driver's or fleet's schedule and load assignments day to day.

Alphabet Soup: CDL, DOT, MC, ELD, HOS, GVWR

A CDL (commercial driver's license) is required to legally operate most truck-and-trailer combinations above a certain weight. A DOT number (issued by the Federal Motor Carrier Safety Administration despite the "DOT" name) identifies a specific motor carrier for safety and inspection records; an MC number (motor carrier number) is a separate identifier tied to a carrier's operating authority to haul freight for hire — a carrier can have one without the other depending on what kind of hauling it does.

An ELD (electronic logging device) automatically records a driver's engine hours and location to track compliance with HOS (hours of service) — the federal rules limiting how many hours a driver can be on duty and driving before a mandatory rest break. GVW (gross vehicle weight) is how much a vehicle actually weighs loaded at a given moment; GVWR (gross vehicle weight rating) is the maximum it's rated to carry — the number that matters for legal loading limits, not the number on any one trip's scale ticket.

Slang You'll Actually Hear on the CB and Around the Yard

A yard jockey (also called a spotter or a shunt truck driver) moves trailers around a distribution yard or dock without ever taking them on the highway, usually driving a low-speed terminal tractor built for exactly that job. A chrome shop is a business that specializes in aftermarket chrome and lighting accessories for trucks — mostly cosmetic, occasionally a whole subculture unto itself. A weigh station (also called a scale house) is where trucks are pulled in to be checked for legal weight and, often, safety compliance.

On the CB radio, a smokey is law enforcement, a four-wheeler is any regular passenger car (as opposed to an "eighteen-wheeler"), the hammer lane is the passing lane, and a parking lot is CB slang for a highway backed up in standstill traffic. None of these terms are official, but you'll hear all of them used matter-of-factly by people who've spent real time around trucks — which is exactly why it helps to know what they mean.