Q: What is a contactless card? Will mine be accepted?
A contactless card is a debit or credit card containing an embedded RFID tag. This allows the card to be used for low value transactions without need for PIN or signature.
TFL say all RFID cards issued by Banks in the UK will work. Cards issued abroad may work, but they're not guaranteeing that.
Note that before your RFID card can be used on the tfl network, it must have been used for at 'contactless' payment at a 'normal' merchant (such as a shop). If you attempt to use your card and it has never been used in 'contact less' mode before, it will be rejected by tfl.