An RFID is a radio frequency identification device. There are two types: active and passive. Some can only be read when they're put near a reader, and some actually emit a little signal.
I don't know if you buy books at Chapters, but occasionally a little square piece of paper will fall out of a Chapters book, and it has a little design thing in it. That's an RFID. If you fly via the airport in Hong Kong, your luggage is tracked by an RFID. They stick it on your luggage and they can track it through the airport. It's being used a lot at the wholesale level to track shipments of goods from the factory to the distributor.