A train was a connected series of vehicles, powered by a Locomotive, and transporting freight or passenger cars along a railroad. Trains were used on Earth until at least the mid-21st century.
After Jonathan Archer restored a damaged timeline, a train could be seen in the time stream as the timeline realigned itself. (ENT: "Storm Front, Part II")
In 1957 T'Mir traveled by train on her way from Carbon Creek to Pittsburgh. (ENT: "Carbon Creek")
Sigmund Freud met Gertrude Stein on a train, the Orient Express. The Orient Express was also the subject of a holodeck simulation enjoyed by Beverly Crusher. (TNG: "Emergence")
Zefram Cochrane preferred taking trains because he disliked air travel (much less going into space). (Star Trek: First Contact)
A primitive unnamed planet visited by Enterprise in 2152 had developed trains. A train-like vehicle was also seen on Dekendi III.
Notable train services