One or more railway vehicles hauled by one or more locomotives or railcars, or one railcar travelling alone, running under a given number or specific designation from an initial fixed point to a terminal fixed point.
A light engine, i.e. a locomotive travelling on its own, is not considered to be a train.
This definition is identical in the third and fourth version of the Transport Glossary.
International Transport Forum, Eurostat, United Nations Economic Commission for Europe (UNECE), "Illustrated Glossary for Transport Statistics", 4th Edition, Luxembourg 2009