The Oyster card is a smart card used for electronic payment on public transport in London. It allows users to travel on the London Underground, buses, trams, the Docklands Light Railway, and some riverboat services. The card can be loaded with pay-as-you-go credit or travel passes, making it a convenient option for both residents and visitors. To use the Oyster card, passengers simply tap it on a card reader at the start and end of their journey. This system automatically calculates the fare and deducts it from the card balance. The card can be topped up at various locations, including ticket machines and online.