Rapid transit in Germany consists of four U-Bahn systems and fourteen S-Bahn systems. The U-Bahn or Untergrundbahn (underground railway) are conventional rapid transit systems that run mostly underground, while the S-Bahn or Stadtschnellbahn (city rapid railway) are commuter rail services, that may run underground in the city center and are classified as metro railways. There are also over a dozen premetro or Stadtbahn systems that are rapid transit in the city center and light rail outside.