An 18-wheeler, also known as a semi-truck or tractor-trailer, is a large vehicle commonly used for transporting goods across long distances. It consists of a tractor unit that houses the engine and a separate trailer that carries the cargo. The name "18-wheeler" comes from the total number of wheels on the vehicle, with 10 on the tractor and 8 on the trailer. These trucks are essential for the freight industry, as they can carry heavy loads and travel on highways. They are equipped with powerful engines and advanced safety features to handle various road conditions. 18-wheelers play a crucial role in the economy by ensuring that products reach stores and consumers efficiently.