Even within a single large city, the suburban railways and the
metro/underground/subway system typically use different terminology.
The appropriate translation and term will always depend on the specific
context, including the specific aspect of the specific rail system are you
talking about and - just as importantly - your specific audience and their
language, country and level of knowledge on your subject.
But don't worry - if you take your time and do your best to be clear, people
who are interested will usually figure out what you're saying in any case.