A trailer is an unpowered vehicle towed by a powered vehicle. It is commonly used for the transport of goods and materials. There are two general categories of trailers: the full trailer and the semitrailer. A full trailer is a type of trailer whose entire weight is supported by its own wheels, with no weight transferred to the towing vehicle. In contrast, a semi-trailer is designed so that a portion of its weight is carried by its own wheels, while the remaining weight is borne by the towing vehicle.
Sometimes recreational vehicles, travel trailers, or mobile homes with limited living facilities where people can camp or stay have been referred to as trailers. In earlier days, many such vehicles were towable trailers.