Train tag usage.

A train is definitonally a coupled set of multiple vehicles, and the wiki page for the tag says this too, but it is often applied to both locomotives on their own and self-propelled railcars/railbusses. Is train a broad catch-all synoynmous with 'rail vehicle', a la ground vehicle, or is it only meant to be used for actual consists?

Everyone calls a single-car train a train.

But not all rail vehicles are trains. Streetcars are not, for instance.