In American and Canadian English, subway refers to a tunnel or other underground structure built to carry mass transit vehicles. Rail rapid transit lines that include subway portions are usually called subway systems. What are generally styled subways in the U.S. or Canada are usually called metros, undergrounds or tubes elsewhere. See also: List of metro systems.
In the UK and Hong Kong, and with older usage in the U.S., a subway (sometimes pedestrian subway) is a pedestriantunnel that goes under a road.
