A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railway locomotive or train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track.
Generally, the types of railway track gauges can be divided into the standard gauge, the narrow gauge, and the broad gauge. The most common gauge is standard gauge 1435mm (4 feet 8 1/2 inches). Gauges narrower than 1435mm are called narrow gauge while wider than 1435mm are called broad gauge.
Monorails are single-rail systems often found in airport transfers and medium-capacity metros. Monorails differ from trams and light rail systems by always being separated from other traffic and pedestrians, and they do not use pantographs.
Tram vehicles are usually lighter and shorter than main line and rapid transit trains. Today, most trams use electrical power, usually fed by a pantograph sliding on an overhead line; older systems may use a trolley pole or a bow collector. In some cases, a contact shoe on a third rail is used.