An evaluated parameter is a numeric value that is evaluated by the library as a constant expression.  This means that the expression can include simple arithmetic, logical, and condition expressions.  It also means that the value of the parameter no longer depends on the source of the parameter.  In other words, if the value is dependent on some macro, it will no longer be dependent on that macro after it is evaluated.  This disables the lazy-evaluation that the preprocessor normallly uses.