The International Union of Railways groups all special classes of railway goods wagon into Class U in its goods wagon classification system.

Goods wagons or freight wagons, also known as goods carriages, goods trucks, freight carriages or freight trucks, are unpowered railway vehicles that are used for the transportation of cargo. A variety of wagon types are in use to handle different types of goods, but all goods wagons in a regional network typically have standardized couplers and other fittings, such as hoses for air brakes, allowing different wagon types to be assembled into trains. For tracking and identification purposes, goods wagons are generally assigned a unique identifier, typically a UIC wagon number, or in North America, a company reporting mark plus a company specific serial number.