The term Multiple Unit (MU) is usually used to describe a passenger train whose carriages have the ability to propel on their own, can be coupled with other similar units to operate together in multiple, and the minimum operating train unit consists of more than one carriages. Depending on the energy source, the two major categories of multiple-unit train are Diesel Multiple Unit (DMU) and Electric Multiple Unit (EMU). If the minimum operating unit consists of only one carriage, it is usually called a Rail Car.