What's the name for a table that does not hold "mutable" data?
It could be called an enum, a reference table or a meta-data table.  

I prefer to call that kind of table by its real name, i.e. in your case "privileges" or perhaps "PrivilegeLevels".  I don't tend to make distinctions between tables where rows change, and tables where rows don't often change since that tends to needlessly add nomenclature for its own sake.