The word “fuzzy” means “vagueness”. Fuzziness occurs when the boundary of a piece of information is not clear-cut.

Fuzzy sets have been introduced by Lotfi A. Zadeh (1965) as an extension of the classical notion of set.

Classical set theory allows the membership of the elements in the set in binary terms, a bivalent condition – an element either belongs or does not belong to the set.

Fuzzy set theory permits the gradual assessment of the membership of elements in a set, described with the aid of a membership function valued in the real unit interval [0, 1].

**Example:**

Words like young, tall, good, or high are fuzzy.

− There is no single quantitative value which defines the term young.

− For some people, age 25 is young, and for others, age 35 is young.

− The concept young has no clean boundary.

− Age 1 is definitely young and age 100 is definitely not young;

− Age 35 has some possibility of being young and usually depends

on the context in which it is being considered.