A train is a form of rail transport consisting of a series of vehicles that usually runs along a rail track to transport cargo or passengers though magnetic levitation trains exist too. 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'.
There are various types of trains that are designed for particular purposes. A train can consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit. The first trains were rope-hauled, gravity powered or pulled by horses. From the early 19th century almost all were powered by steam locomotives.