[Fuzzy logic is] a logic whose distinguishing features are (i) fuzzy truth-values expressed in linguistic terms, e. g., true, very true, more or less true, or somewhat true, false, nor very true and not very false, etc2.; (2) imprecise truth tables; and (3) rules of inference whose validity is relative to a context rather than exact.

Zadeh (1975) "Fuzzy logic and approximate reasoning". Synthese 30: p. 407