Arity

Arity is the number of arguments or operands taken by a function, operation or relation. A function that takes no arguments is called nullary, one that takes a single argument is unary, one that takes two arguments is binary, and one that takes three is ternary, with the general case for n arguments called n-ary. Common binary operations include ordinary addition and multiplication, and many programming languages include a ternary conditional operator. In mathematics arity is sometimes called rank, in logic and philosophy it is sometimes called adicity or degree, and the closely related idea is called valency in linguistics.