a shortened form of if and only if: it indicates that the two sentences so connected are necessary and sufficient conditions for one another. Usually iff is used for equivalence in the metalanguage, rather than as the biconditional in the object language
IFF in British English
military
abbreviation for
Identification, Friend or Foe: a system using radar transmissions to which equipment carried by friendly forces automatically responds with a precoded signal
IFF in American English
Identification, Friend or Foe: an electronic system for recognition of friendly aircraft, ships, etc.
Examples of 'iff' in a sentence
iff
His IFF transponder was switched off at the moment, and he was able to relax and enjoy the ride, something he almost always did.