The Oyster Card
The Oyster card is a credit-card-sized stored-value contactless smart card for public transport in London.
It is promoted by Transport for London (TfL) and can be used on travel modes across London including London Underground, London Buses, the Docklands Light Railway (DLR), London Overground, Tramlink, some river boat services, and most National Rail services within the London fare zones.
Since its introduction in June 2003, more than 86 million cards have been used.
It is widely used today and as commerce begins to go cashless (London Buses are now cashless), the card supports tens of thousands of permutations of travel through a single payment option to tap at the point of entry to your transport choice.