exitcode is the variable identifier for a built-in variable of type integer, whose value is returned to the calling program when your program exits.
For example, suppose you want to return a value of 1 from your program (perhaps to indicate that your program detected an error) then you can use the following code
exitcode := 1; halt;
NOTE: You can treat exitcode like any other integer variable (i.e. you can assign integer values to it, use it in an expression, pass it as an argument to a function, etc).
Operating Systems: All Standard Pascal: No