Transceiver, a combined transmitter and receiver. ie. walky talkies. Bluetooth adapter, a MAX232 level shifter.
Transponder, a device that when interrogated will respond with the relevant information. For example, a digital temperature chip will reply with a data stream that represents the temperature when commanded to do so. An aircrafts transponder will report the call sign and height of an aircraft when interrogated by an airport radar (squawk and mode C for any pilots present :roll: ).
Neither have to be radio. Both could be radio, IR, ultrasonic, sonar etc.
Mike.