Monorail

A monorail is a railway in which the track consists of a single rail. The term is also used to describe the beam of the system, or the vehicles traveling on such a beam or track. The term originates from joining "" (one) and "rail" (rail), from 1897, possibly from German engineer Eugen Langen, who called an elevated railway system with wagons suspended the Eugen Langen One-railed Suspension Tramway (Einschieniges Hängebahnsystem Eugen Langen).

Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurately, the term refers to the style of track, not its elevation, with 'Mono' meaning 'one,' and 'Rail' meaning 'rail.'

Monorails have found applications in airport transfer and medium capacity metros. To differentiate monorails from other transport modes, the Monorail Society says “Monorail n. 1. A single rail serving as a track for passenger or freight vehicles. In most cases rail is elevated, but monorails can also run at grade, below grade or in subway tunnels. Vehicles either are suspended from or straddle a narrow guide way. Monorail vehicles are wider than the guide way that supports them.”

Monorails are often elevated, sometimes leading to confusion with other elevated systems such as the Docklands Light Railway, Vancouver SkyTrain and the AirTrain JFK, which run on two rails.

Monorail vehicles often appear similar to light rail vehicles, and can be staffed or unstaffed. They can be individual rigid vehicles, articulated single units, or multiple units coupled into trains. Like other advanced rapid transit systems, monorails can be driven by linear induction motors; like conventional railways, vehicle bodies can be connected to the beam via bogies, allowing curves to be negotiated.

...
Wikipedia