What does the term “multiple unit” or “MU” mean, and what is an EMU or DMU?
There are two senses of the phrase “multiple unit” to be distinguished. Two or more regular locomotives may be coupled together for greater hauling capacity. In such a cases the locos are said to be operating as multiple units, or to be “MU’ed together” (US terminology: “lash-up”). This is not to be confused with the terms electric multiple unit (EMU) or diesel multiple unit (DMU) which refer to cars used for (mostly suburban) train services which have multiple prime movers (either electric motors or diesel engines) for each car. I.e., the same car that carries passengers also has the motive power, as opposed to the normal situation where the passengers are in coaches that are not self-propelling and a locomotive hauls the train.
