What is the difference between MEMU and DEMU trains?

MEMU Trains are rapid transit trains operated by Indian Railways. MEMU stands for Mainline Electric Multiple Unit.

The Mainline Electric Multiple Unit or MEMU is a commuter rail system in India operated by the Indian Railway for semi-urban and rural areas. The first MEMU service in Bilaspur division of S E Railway started on 17-10-1995 in 1995-96 between Raipur-Durg-Bhatapara-Raipur-Bilaspur. First train was inaugurated by V.C.Shukla, the senior leader of Indian national congress. The system uses Mainline Electrical Multiple Units (MEMU) operating on Alternating Current (AC) drawn from over-head cables through the catenary system. MEMU trains are designed for semi-urban and rural areas, unlike EMU (electric multiple unit) trains that are designed for urban and semi-urban areas.

DEMU stands for Diesel Electric Multiple Unit, rapid transit trains operated by Indian Railways on suburban network. A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. A DMU requires no separate locomotive, as the engines are incorporated into one or more of the carriages. Diesel-powered single-unit railcars are also generally classed as DMUs. Diesel-powered units may be further classified by their transmission type: diesel–electric (DEMU), diesel–mechanical (DMMU) or diesel–hydraulic (DHMU).

The diesel engine may be located above the frame in an engine bay or under the floor. Driving controls can be at both ends, on one end, or in a separate car.
DEMU and MEMU are examples of Multiple Unit which are self propelled train carriages which when coupled with other Multiple Units can be controlled by a single terminal.

MU train is not hauled (pulled) by separate locomotive.

Multiple Units are classified on the basis of source of power:

EMU/ MEMU: Electric Multiple Units.

DMU: Diesel Multiple Units; DMUs are further classified on the basis of form of transmission of motive powers to the wheels into:

DEMU: Diesel Electric Multiple Unit
DMMU: Diesel Mechanical Multiple Unit
DHMU: Diesel HydraulicMultiple Unit.