Where does the name semi truck come from?

Semi truck is derived from semi trailer, which is short for semi-trailer truck. The term semi-trailer refers to the fact that only the front half of the truck, known as the tractor, is motorized. The rear half, known as the trailer, is not powered and is attached to the tractor via a fifth wheel coupling. The name "semi truck" is most commonly used in North America, while other regions may use different terms such as articulated lorry, articulated truck, or tractor-trailer.