In rail transport, a train consists of rail vehicles that move along guides to transport freight or passengers from one place to another. The guideway (permanent way) usually consists of conventional rail tracks, but might also be monorail or maglev. Propulsion for the train is provided by a separate locomotive, or from individual motors in self-propelled multiple units. Most trains are powered by diesel engines or by electricity supplied by trackside systems. Historically the steam engine was the dominant form of locomotive power through the mid-20th century, but other sources of power (such as horses, rope (or wire), gravity, pneumatics, or gas turbines) are possible.

In American railway terminology, and increasingly within the railway industry in the United Kingdom, a consist is used to describe the group of rail vehicles which make up a train.

Types of Trains

There are various types of trains designed for particular purposes. A train can consist of a combination of a locomotive and attached railroad cars, or a self-propelled multiple unit (or occasionally a single powered coach, called a railcar). Trains can also be hauled by horses, pulled by a cable, or run downhill by gravity.

Special kinds of trains running on corresponding special 'railways' are atmospheric railways, monorails, high-speed railways, Dinky Trains, maglev, rubber-tired underground, funicular and cog railways.

A passenger train may consist of one or several locomotives, and one or more coaches. Alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered as a "multiple unit". In many parts of the world, particularly Japan and Europe, high-speed rail is utilized extensively for passenger travel.

Freight trains comprise wagons or trucks rather than carriages, though some parcel and mail trains (especially Travelling Post Offices) are outwardly more like passenger trains.

In the United Kingdom, a train hauled by two locomotives is said to be "double-headed", and in Canada and the United States it is quite common for a long freight train to be headed by three, four, or even five locomotives. A train with a locomotive attached at each end is described as 'top and tailed', this practice typically being used when there are no reversing facilities available. Where the second locomotive is attached temporarily to assist a train up steep banks (or down them by providing braking power) it is referred to as 'banking'.

Trains can also be mixed, hauling both passengers and freight, see e.g. Transportation in Mauritania. Such mixed trains became rare in many countries, but were commonplace on the first 19th-century railroads.

Special trains are also used for Track Maintenance; in some places, this is called maintenance of way.

A single uncoupled rail vehicle is not technically a train, but is usually referred to as such for signaling reasons.