The name of a function generally indicates something about what task the function actually performs. Values input into a function are termed arguments to the function, or function arguments. These values enter a function through its lambda parameters. Once a function has finished its computation it outputs its results. Output from a function is often referred to as the return value, or value of the function.
Lisp functions have the ability to return more than one value as a result.
In general then, we can think of a function as something that provides a mapping between inputs and outputs. The exact number of inputs and outputs a function uses is determined by the programmer when the function is defined. Function Calls Passing input values to a function and receiving its output values is referred to as calling a function, or applying a function to its arguments. Since each argument is evaluated, input values can be specified in terms of function calls. This sort of nesting is very typical in Lisp programming.