(mathematical analysis) A function which is equal to 1 for all points in its domain which belong to a given set, and is equal to 0 for all points in the domain which do not belong to that given set.

(mathematical analysis) A function which is Borel measurable.

(mathematics) A linear mapping from a vector space to its field of scalars.

(physiology) A normal physical process that occurs in the body. / (euphemistic) An excretory function of an organism, usually the discharging of feces and urine.

(biology) Any function of the body that is essential for maintaining life, especially breathing and circulation.

(mathematics) a type of function used in the analysis of inhomogeneous differential equations.

(mathematics, cryptography) A function that is easy to compute in one direction but difficult to compute in the opposite direction (finding its inverse) without special information.

(mathematics, statistics) A sigmoid function giving the probability that a measurement, under the influence of normally distributed errors with standard deviation, is within a certain distance from the mean value.

(computer science) A mathematical function that can be computed using an abstract computation machine such as Turing machine.

(mathematics) A unary function that preserves the addition operation; a unary function f such that for any x and y: f(x + y) = f(x) + f(y).