Those huge vehicles overwhelming the highways are called tractor semi-trailers because the back portion sits on wheels while the front end is supported by the tractor.
A full trailer rides on its own wheels with axles on the front and back and is connected to the tractor by a drawbar.
Sometimes a full trailer is attached to a semi, which is attached to the tractor.
A truck doesn’t have any attachments.
And that’s the difference between a truck, a tractor semi-trailer, and a full tractor-trailer.