Here's the breakdown:
* "Ex" - meaning "out" or "from"
* "Folium" - meaning "leaf"
* "-atus" - a past participle ending, meaning "having been..."
So, literally, "exfoliatus" means "having been stripped of leaves."
This original meaning is fitting because the word "exfoliate" refers to the process of removing dead skin cells, much like a tree sheds its leaves.