In article , (Aidan Stanger) wrote:

As Germany has (over the last few years) gained several Stadtbahnen
(light rail lines) which are quite different from S-bahnen, I don't
believe you!

Collins gives S-Bahn as abbreviation of either Stadtbahn or Schnellbahn,
and the definitions as respectively "high-speed railway" (which IMO is never
what an S-Bahn is!) and "suburban railway (Brit), city railroad (US)."

The online dictionary http://dict.leo.org gives quite a selection for Stadtbahn:

city railway, light rail link, light rail rapid transit, light rail transit, light railway,
metropolitan railway

....and interestingly, for commuter railway system, urban-suburban commuter
railway system, "S- und Stadtbahn", which indicates that whatever "S-" means
there, it's not "Stadt-"! Perhaps it's just a word now with its original significance
no longer there, like BAA or BT? On the other hand, for "light rail transit" among
other things it gives "Stadtbahnen und Straßenbahnen", and for "underground
light railway" "Unterpflasterstraßenbahn".

There is often an overlap between street-running trams and underground rapid
transit, e.g. in Cologne or Boston (Mass.).

--
Peter Beale