http://foldoc.org/argument even includes the distinction between "formal argument" and "actual argument".

For the situations you seem to be describing, I tend to use an adjective rather than a noun so that the noun can clarify the type of argument. "The passed-in string will be made all upper case" or "The specified subdirectory will be created" or "given".

Interestingly, Foldoc defines parameter as a synonym only for "formal argument" even though I use it and see it used as "actual argument" quite often.