logic 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
—abbreviation for
Identification, Friend or Foe: a system using radar transmissions to which equipment carried by friendly forces automatically responds with a precoded signal
mathematics, logic if and only if, i.e. necessary and sufficient. For example, two figures are congruent iff one can be placed over the other so that they coincide. (2002-12-28)