What is function arity?

Function arity refers to the number of parameters or arguments that a function takes. For example, a function with arity 0 takes no arguments, a function with arity 1 takes one argument, and a function with arity 2 takes two arguments. Arity can be important when working with programming languages that require explicit type signatures or when working with higher-order functions that take functions as arguments or return functions as results. Additionally, arity can affect the way that functions are called or composed, as functions with different arity may require different approaches to calling or be difficult to compose.