Function Parameter vs. Argument — Computer Science Atlas

When talking about functions, the words "parameter" and "argument" may appear at first to be interchangeable. However, for many programming languages, the words actually refer to two different things. In short:

A parameter is part of the function's definition: an input that the function expects.
An argument is part of a function call: a value passed to the function to satisfy one of the parameters required by the function definition.

For example, if we have the following function definition in JavaScript:

JavaScript

/*  Parameters: a, b  */
function add( a, b ) {
    return a + b
}

1
2
3
4
/*  Parameters: a, b  */
function add( a, b ) {
    return a + b
}

a and b are parameters of the function add.

If we then call the function:

JavaScript

/*  Arguments: 2, 3  */
let sum = add( 2, 3 )

1
2
/*  Arguments: 2, 3  */
let sum = add( 2, 3 )

2 and 3 are arguments of the add( 2, 3 ) function call statement. The argument 2 satisfies parameter a, and argument 3 satisfies parameter b.

Reference

Many popular programming languages today derive their usage of the terms from earlier sources like:

Section 1.7, Functions, in Kernighan, Brian W., and Dennis M. Ritchie, The C Programming Language, 2nd ed., Prentice Hall PTR, 1988, p. 25. This book is often called "K & R" (the initial letters of its authors' last names).