Iff Definition
abbreviation
If and only if.
American Heritage
Identification, Friend or Foe: an electronic system for recognition of friendly aircraft, ships, etc.
Webster's New World
(mathematics, logic) If and only if; used to show that the predicate that follows it has the same truth value as the predicate that precedes it.
Wiktionary
Identification friend or foe.
Wiktionary
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