In computer programming, a parameter or "argument" is a value that is passed into a function. Most modern programming languages allow functions to have multiple parameters. While the syntax of a function declaration varies between programming languages, a typical function with two parameters may look something like this:
function graphXY(x, y)
When this function is called within a program, two variables should be passed into the function. It may look something like this:
$horizontal = 22;
$vertical = 40;
In this example, the values 22 and 40 (stored in the variables $horizontal and $vertical respectively) are the "input parameters" passed into the graphXY() function.
When a function has input parameters, the output of the function is often affected by the values that are passed into the function. Therefore, a single function can be called multiple times within a program and produce different output each time.