Why is a 18 wheel truck called semi?
An 18-wheeler is not called a semi. The term "semi" is used to refer to a semi-trailer truck, which is a type of commercial vehicle that consists of a tractor and a semi-trailer. The tractor is the front part of the truck that includes the engine, cab, and front wheels, while the semi-trailer is the towed part that carries the load. An 18-wheeler is a type of semi-trailer truck that has 18 wheels, but not all semi-trailer trucks are 18-wheelers.