The Free On-line Dictionary of Computing (19 January 2023):
IFF 1.Interchange File Format. 2. Identify friend or foe (radar). The Free On-line Dictionary of Computing (19 January 2023):
iffif 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)