A semitrailer is a type of truck trailer that is designed to be pulled by a tractor unit. It consists of a large cargo-carrying platform, typically supported by wheels at the rear and a fifth wheel coupling at the front, which connects to the tractor. Semitrailers are commonly used in transportation and logistics industries for carrying goods over long distances. They come in various sizes and configurations to accommodate different types of cargo, and they play a crucial role in the global supply chain.