Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point. These overhead lines are known variously as
Overhead contact system (OCS)—Europe, except UK and Spain Overhead line equipment (OLE or OHLE)—UK Overhead equipment (OHE) — UK, India, Pakistan and Malaysia Overhead wiring (OHW)—Australia Catenary—United States, India, UK, Singapore (North East MRT Line), Canada, France (:fr:Caténaire), Spain and Portugal (:pt:Catenária_(caminho_de_ferro)).
In this article the generic term overhead line is used. This is also the term used by the International Union of Railways.
Overhead line is designed on the principle of one or more overhead wires or rails (particularly in tunnels) situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid.