A train consists of rail vehicles that move along guides to transport freight or passengers from one place to another. The guide way (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, but other sources of power such as steam engine, horses, wire, gravity, pneumatics, or gas turbines are possible.
Rail transport remains the most energy efficient land transport, and used for long-distance freight and all distances of passenger transport. In cities rapid transit and trams are common parts of public transport.