This function returns the name of the resolution with the given id.
resolution(id) #Output: Text
You might want to use this function for several parser expression where you are e.g. checking against the current resolution. So even if you rename the resolution afterwards, the parser expression still works and won't break.
Imagine an expression like this:
%{issue.resolution} = resolution(10000)
instead of:
%{issue.resolution} = "Won't fix"