A transport system using rails used to move passengers or goods.
A track, consisting of parallel rails, over which wheeled vehicles such as trains may travel.
An underground railway, especially for mass transit of people in urban areas.
An underground route for pipes, sewers, etc.
A rapid transit system, regardless of the elevation of its right of way; a metro system.
A train that runs on such an underground railway.
An underground walkway, tunnel for pedestrians (called pedestrian underpass in US).
To travel by underground railway.