An Oyster card is a plastic credit card sized 'smart card' which is accepted by Transport for London (TfL) as a ticket for travel with the London Fare Zones. The card has a micro-chip embedded within it that is capable of storing and conveying details of electronically stored season tickets i.e. 'in-boundary" travelcards and TfL Bus Passes.
The chip also records details of money added to the card, known as pay as you go (PAYG). The card holder can use PAYG to travel on both TfL and participating National Rail services.
The Oyster card is neither a travel document, a ticket or a permit to travel. Nor is it a credit card or debit card. It is simply a way of storing a ticket such as a Travelcard season, and a cash value for payment of single journeys. For more information, why not visit the Transport for London (TfL) website.