What's the name for a table that does not hold "mutable" data? Let's say I have a users table, and each user has a different level of privilege. I have a privileges table with four rows that looks like this:

id | level
---+-----------
1  | viewer
2  | editor
3  | admin
4  | super-admin


In the business context, my users all have a privilege level, 1-4. The users table holds the corresponding user data, and it gets modified when users are modified, added, or dropped, but privileges never really changes, it is just a reference of the four established privilege levels. 

Is there a name or term for this type of table?
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.