A semi-trailer doesn’t have a front axle while a large portion of its weight is handled by a tractor unit. They are called ‘semi-trailers’ because (unlike full trailers) there are no front wheels and they can only be moved when attached to the tractor unit. Therefore, semi-trailers usually have legs to support them when they are not in use. The name semi-trailer was adapted over time and is now what most people in the UK call them. When it comes to navigating, a semi-trailer has a much smaller turning circle than a full trailer, which makes it more manageable on European roads.