A siding, in general rail terminology, refers to a section of rail used to store stationary rolling stock perhaps whilst it is loaded or unloaded, or alternatively, a short length of rail that provides access to and from factories, mines, quarries, wharves, etc. A group of sidings in one ownership may be termed a marshalling yard.
A siding can also refer to a stretch of rail tracks that provides a place for a train to stay temporarily while other trains pass on the main line. In British terminology, this latter example is termed a passing loop. This configuration allows the sequence of trains along a track to change and trains or trams to pass one another where a route is predominantly single tracked.
A siding, in general rail terminology, refers to a section of track distinct from a through route such as a main line or branch line or spur.
Such "industrial sidings" might be found at factories, mines (mining), quarries, wharves, warehouses, etc. Such sidings can sometimes be found at stations for public use; in American usage these are referred to as team tracks (after the use of teams of horses to pull wagons to and from them).
Passing sidings, as the name implies, are constructed to allow one train to pass another, and are thus an essential feature of single track lines.