A larger portion of the cargo's weight in a semi-trailer is supported by the tractor unit in the front and the rest is by its own wheels in the rear.
The axles of the semi-trailer are all on the rear part of the trailer.
A semi-trailer has to be supported by landing gear in the front when detached from the truck unit as it could not stand only by the wheels in the rear.
It combines with the truck unit in the front and is also referred to as a semi-trailer truck or just "semi" in North America.
There are many types of semi-trailers with different functions, like fuel trailers, flatbed trailers, chemical trailers, storage pig trailers, etc.
The semi-trailers are commonly used in logistics for long-distance transport.
The complete weight of the trailer and the loaded cargo is supported by the full trailer itself.
Both the front and the rear part of the trailer has an axle.
The full trailer could stand and bear the weight by itself without requiring a landing gear/leg.
The truck or the tractor unit only hauls the trailer and provides traction steering.
The full trailers are normally used in factories, ports, terminals, warehouses, etc.
The full trailers are commonly used for short-distance transport.