Metro
From Citizendium, the Citizens' Compendium
Metro is a general term for an urban transportation system, which can include underground train systems but is not limited to it. Other components can include wheeled busses and light rail systems that run on streets. Heavy rail runs on dedicated tracks, which may be at ground level or elevated above it, as in the "El" of Chicago. A few systems have more exotic transportation components such as monorails and magnetically levitated trains.
An underground urban component is called "underground" in British English, but may be called "Metro" in many languages, and "subway" in American English.
Metro systems often interconnect with long-haul transportation systems, including bus, train and air.
