Radio Frequency Identification

the use of radio signals to recognize, from a few feet away, a tiny device ("RFID tag") that can be built into price tags, library books, parking permits, or the like. RFID tags are even implanted under the skin of dogs for positive identification so that they can be returned to their owners if lost and found.

The RFID tag consists of an antenna and an integrated circuit, but no battery. The antenna picks up enough power from the transmitter that it can energize the integrated circuit and transmit a response, typically just an identifying number. The RFID tag itself contains almost no information; its usefulness comes from a database linking its ID number to other records.