A type of logic based on the concept of real-valued, continuous truth values (within the closed interval $[0,1]$). Contrary to classical, binary logics, where only the truth values ${0, 1}$ apply, fuzzy logic allows to express uncertainties.
ETSI GR ENI 004 fuzzy logic: type of many-valued logic that allows a truth value to be any real number between 0 and 1 inclusive.
NOTE: Fuzzy logic is most often used to reason about the degree of truth, or probability, in a system.
ISTQB - CTAI Syllabus A type of logic based on the concept of partial truth represented by certainty factors between 0 and 1