The term multiple unit is used to describe a self-propelled carriages capable of coupling with other units of the same type.
The term multiple unit or MU is used to describe a self-propelled carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. The term is commonly used to denote passenger trainsets consisting of more than one carriage. Single self-propelling carriages (also called railcars, rail motor coaches or railbuses) can be referred to as multiple units if capable of operating with other units.Multiple units are classified by their power source and are of two main types: electric multiple unit (EMU) or diesel multiple unit (DMU). Diesel-powered units may be further classified by their transmission type: diesel-electric (DEMU), diesel-mechanical (DMMU) or diesel-hydraulic (DHMU).Locomotives utilising multiple-unit train control are not multiple units.