(linear algebra) A diagonal matrix all of the diagonal elements of which are equal to 1.

(mathematics) A function whose value is always the same as its independent variable, and for which the codomain equals the domain.

(complex analysis) The equation e^(i𝜋)=-1,!, which unifies diverse fields of mathematics.

(psychology) A crisis of personal identity.

plural of identity theft

A card or badge showing the official identity of the bearer.

(philosophy) The principle that, if two objects are indistinguishable from one another with respect to all of their properties, then they are identical.

plural of identity card

(psychology) A person's internal sense of self as belonging to a particular gender or genders, or to no gender.

plural of standard of identity