A train is a form of rail transport consisting of a series of vehicles propelled along a rail track to transport cargo or passengers. Motive power is provided by a separate locomotive or individual motors in self-propelled multiple units. Although historically steam propulsion dominated, the most common modern forms are diesel and electric locomotives, the latter supplied by overhead wires or additional rails. Other energy sources include horses, rope or wire, gravity, pneumatics, batteries, and gas turbines. Train tracks usually consists of two, three or four rails, with a limited number of monorails and maglev guideways in the mix. The word 'train' comes from the Old French trahiner, from the Latin trahere 'pull, draw'.
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, railroad ties (sleepers, British English) and ballast (or slab track), plus the underlying subgrade. For clarity it is often referred to as railway track (British English and UIC terminology) or railroad track (predominantly in the United States).
The term permanent way also refers to the track in addition to lineside structures such as fences etc.