Multiple unit
Also: unit, emu, dmu
A train with its motors built into the carriages, so there’s no separate engine pulling it.
Most passenger trains in Britain are multiple units: a fixed set of carriages with motors underneath and a driving cab at each end. They can drive either way, so they don’t need turning round.
An EMU is electric, taking power from overhead wires or a third rail. A DMU carries its own diesel engines. A bi-mode can do both, running on electric where there are wires and diesel where there aren’t.
Units can couple together to make longer trains, and split apart again on the way.