Railway station
A railway station is a facility found on railways (or railroads in some parts of the USA), which serves as the point where passengers board and alight trains. They can vary massively in size and importance, from small halts with a single platform and no structures to major termini with dozens of platforms and adjoining shops and facilties.
Railway stations usually have facilities for passengers to buy tickets (a booking office), a waiting area, and possibly baggage handling facilities. Stations can be located underground or on sections of elevated track.
Union Stations
In the United States, a Union Station is one where tracks owned by multiple railroad lines merge. Prior to nationalisation, such a station in the United Kingdom was referred to as a Joint Station.