What is a semi-trailer
A semi-trailer is a functional part of a tractor-trailer combination.
Any type of semi-trailer, such as a reefer, dry van, or a flat bed, can be attached or detached from a tractor.
When it is detached, it cannot move because a semi-trailer doesn’t have an engine. So, to move it needs to be connected to a tractor.
This is the main way how they function. Semi-trailers are loaded, picked up by a semi-truck, and they are on the way to delivery.
Below, find more information about semi-trailers.

Why are semi-trailers so commonly used?
What are semi-trailers used for - find out how are different types of semi-trailers designed to be used and what kind of freight to transport.
Semi-trailer vs full-trailer - find out what are the differences between the two types of trailer configurations.

Understanding the different semi-trailer types?
Semi-trailer dimensions - find out the different dimensions and capacities for different semi-trailer types.
Semi-trailer brands - find out a list of semi-trailer manufacturers in the US.
Truck-trailer types - find a list of different types of semi-trailer.