A monorail is a railway in which the track consists of a single rail, typically elevated. 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 mono (one) and rail (rail), from as early as 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' being the Greek numeral prefix for one and 'Rail' meaning 'rail' structure utilized.(Wikipedia)