fuzzy logic

n. A branch of mathematics in which items have probabilities of being included in any set rather than clearly defined membership. Thus some items have higher probabilities of being included in a set than others, and items may have nonzero probabilities of being included in two sets that would be mutually exclusive were they defined by either-or rules. This theoretical approach has been widely used in computer science, where it finds applications in control and expert systems. It has also been used to model the prototype approach to human categorization.