S-Bahn is a city center and suburban metro like railway system in Austria, Germany, Switzerland and Denmark. The Copenhagen S-tog (English: S-trains) refers to trains rather than tracks, but is otherwise the same.
Read more about S-Bahn: Name and Some History, Train and Station Logotypes, Definition: S-Bahn and Heavy Rail, S-Bahn in "mid-size" Cities, Other Similar System, Similar Systems in Other Countries