Semi-trailer truck
A semi-trailer truck is the combination of a tractor unit and one or more semi-trailers to carry freight. It is variously known as a transport (truck) in Canada; semi or single in Australia; semi, tractor-trailer, big rig, or eighteen-wheeler in the United States; articulated lorry, abbreviated artic, in Britain and Ireland.
A semi-trailer attaches to the tractor with a fifth wheel hitch, with much of its weight borne by the tractor. The result is that both tractor and semi-trailer will have a distinctly different design than a rigid truck and trailer.
Regional configurations
North America
In North America, the combination vehicles made up of a powered truck and one or more detachable trailers, are known as semi-tractor-trailers, tractor-trailers, semis, big rigs, semi trucks or eighteen-wheelers.
Trucks
The tractors, or powered trucks, typically have two or three axles; those built for hauling heavy-duty commercial-construction machinery may have as many as four or five axles, some often being lift axles.