An unmodified stat is your characters stat before wearing any rings, amulets, enchants, etc.
In the past, spell effectiveness was based on something like (unmodified intelligence / 25).
I don't think anything in the game should depend on unmodified stats (except learning new skill books).
If someone makes a really dumb giant with 2 intelligence, they should be able to wear a ring of intelligence and bring their intelligence up to 5. The game shouldn't continue to use their original 2 intelligence when computing spell duration and spell damage, etc. Same goes for any other stat (str, dex, int, end) which the game is secretly using the unmodified value.
If modified stats are "too high" for game formulas then the game can use (modified stat - a small constant) instead of using (unmodified stat).
Using modified stats gives all of our characters more choice and flexibility and it's easier to understand.