"DMU"

DMU is an abbreviation for Diesel Multiple Unit. It commonly covers diesel powered units with two types of transmission, mechanical (DMMUs) and hydraulic (DHMUs). Normally differentiated, vehicles with electric transmission are referred to as DEMUs.

"Multiple"

Diesel Multiple Units, as the name implies, are designed to run in units (sometimes called sets) normally comprising powered vehicles and trailer cars. There are many different formations possible, although the common arrangement being two powered cars with a trailer car in the middle or one power car and one trailer, although many other formations have been used. These units can be worked in multiple with other units with the same coupling code, up to a maximum of six power cars, depending on the control system design.

"Railcar"

When these trains were introduced in the '50s, they were first referred to as "(lightweight) Diesel Trains", but they soon became more commonly known as alternatively "diesel railcars" or "DMUs", as well as many other derogatory names!

Further information can be found at www.railcar.co.uk.