(mathematics) Any function whose value may be directly calculated from the independent variable.

(mathematics) Any function that is composed of algebraic functions, trigonometric functions, exponential functions and/or logarithmic functions, combined using addition, subtraction, multiplication and/or division

(mathematics) Any function of a complex variable which is periodic in two directions.

(mathematics) Any function in which an independent variable is in the form of an exponent; they are the inverse functions of logarithms

An electronic analog computing device that accepts as input two periodic functions and outputs their mathematical product

(computing) Any of a set of keys on a personal computer or terminal keyboard used to activate a predefined or programmable function.

(mathematics) Any function whose value is unchanged if the independent variable changes sign i.e. f(x) = f(-x)

(mathematical analysis, algebraic geometry) A function defined by a (multivariable) implicit equation when one of the variables is regarded as the value of the function, especially where said equation is such that the value is not directly calculable from the other variables.

(management) Any primary business function that would affect customers or profits if interrupted

(mathematics) Any function whose graph is a straight line: f(x)=ax+b