A pocket track, tail track, or reversing siding is a rail track layout which allows trains to park off the main line. This type of track layout differs from a passing loop in that the pocket track is usually located between two main lines, rather than off to the side. Found primarily on metro systems, rapid transit light rail networks, and tramways, a pocket track allows certain trains or trams to change direction, even on lines with high traffic flow, while others continue through the station.