Unlike full trailers, semi-trailers have their axles positioned behind the vehicle's center of gravity (when uniformly loaded) and are equipped with a coupling device capable of transmitting horizontal or vertical forces to the towing vehicle; generally, full trailers have two axles, whereas semi-trailers have one. A semi-trailer is a vehicle that lacks its own power source and relies on a towing vehicle (tractor unit) for propulsion, sharing the load with the tractor.
Simply put, a full trailer connects to the truck ahead via a tow hitch. A semi-trailer connects to the tractor unit's fifth-wheel coupling via a kingpin; a common container transport vehicle is a classic example of a semi-trailer combination, where the rear cargo-carrying section is the semi-trailer itself.
There are also differences in application: full trailers are primarily used for short-distance transport within sites such as factories, ports, terminals, and warehouses, while semi-trailers are mainly used for long-distance cargo transport.
