The Elizabeth line is a high-frequency hybrid urban–suburban rail service in London and its suburbs. It runs services on dedicated infrastructure in central London from the Great Western Main Line west of Paddington station to Abbey Wood and via Whitechapel to the Great Eastern Main Line near Stratford; along the Great Western Main Line to Reading and Heathrow Airport in the west; and along the Great Eastern Main Line to Shenfield in the east. The service is named after Queen Elizabeth II, who officially opened the line on 17 May 2022 during her Platinum Jubilee year; passenger services started on 24 May 2022. Despite being named under the same system as London Underground lines, and having sections which are underground, the Elizabeth line is not classified as a London Underground line.

Commuter rail, or suburban rail, is a passenger rail transport service that primarily operates within a metropolitan area, connecting commuters to a central city from adjacent suburbs or commuter towns. Commuter rail systems are considered heavy rail, using electric or diesel trains. Distance charges or zone pricing may be used.