Radio-frequency identification (RFID) uses radio waves to automatically identify objects. RFID tags contain antennas that receive and respond to an interrogator's signals. RFID tags can be classified as active, passive, or semi-passive. An RFID system consists of tags, a reader with an antenna, and backend software. RFID is used for applications like supply chain management, asset tracking, and access control. While offering advantages like contactless identification, RFID also raises privacy and security concerns that require consideration.