An electric multiple unit or EMU is a multiple unit train that requires no separate locomotive and uses electricity as the motive power. Usually formed of two or more semi-permanently coupled carriages, most EMUs are used for passenger trains though it is not uncommon for them to be used for specialized non-passenger purposes. A diesel multiple unit or DMU, on the other hand, is a multiple-unit train powered by on-board diesel engines. Like EMU, DMUs also require no separate locomotives. The different types of DMUs can be diesel-electric (DEMU), diesel-mechanical (DMMU) or diesel-hydraulic (DHMU). These trains are popular throughout the world as they conveniently allow passenger capacity to be matched to demand. Contrasting with the EMU and DMU is the Mainline Electric Multiple Unit or MEMU which is generally operated in the semi-urban and rural areas in India. MEMU trains have lavatories and end vestibules (gangway connections) not found on EMU trains.