(astronomy) A function that describes the angular distribution of light reflected from a body when illuminated from a specific direction

(mathematics) A generalization of the indicator function for a fuzzy set which assigns a truth value (0 or 1) to each element.

(computing) Any function that uses recursion and can call itself until a certain condition is met

(mathematics, complex analysis, algebraic geometry) Any function expressible as the quotient of two (coprime) polynomials (and which thus has poles at a finite, discrete set of points which are the roots of the denominator).

(mathematics) A function of one or more independent variables, at least one of which is itself a function of one or more other independent variables; a function of function(s).

(computing) Any function that is provided as part of a high-level language and can be executed by a simple reference with specification of arguments

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

(mathematics) Any function that is a solution of the hypergeometric equation; usually an expansion of an hypergeometric series

(mathematics) Any function that possesses a finite integral

(computing) A function used in an operating system that is not available to application programs.