In telecommunication, identification, friend or foe (IFF) is a system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces.
The primary use of the term is to describe an aviation subsystem that permits military aircraft, and both civilian and military air-traffic controllers, to identify aircraft as enemy and friendly, and track them.
- in a civilian aircraft, by sending a code identifying it;
- in a military aircraft, by sending, only when detecting a code indicating the radar is part of the friendly-forces' network, a similarly coded signal.
- Avoiding "friendly-fire" or "fratricidal" attacks
- Reducing attacks on civilian aircraft
- Improving, by coordination among friendly forces, decisions about tactics.