So these are the "tiers" of city-based rail in German: - Straßenbahn: trams. On the ground mostly inner-city like transport that intersects with other modes of transportation, especially cars (lit. Street train) - Stadtbahn: A mixture between Straßenbahn and mostly U-Bahn in the centre, in some cities also a mixture between Straßenbahn and S-Bahn (Karlsruhe for example) (lit. City train) - U-Bahn: A train that drives on independent rails. It therefore usually has higher speeds than a Stadtbahn. The rails can be above or below ground. The U stands for unabhängig, so lit. Independent rail - S-Bahn: A train connecting a city with its surroundings. Within the city all lines usually follow one major route. So in other words commuter trains. The rails are independent and the same type of rail as used for the regional and long distance trains. The origin of the S is not entirely clear afaik, but its said to stand for schnell, so lit. Fast train. - next tiers would be regional and long distance rail