Exfoliation is the process of removing dead skin cells on the skin. There are two methods in which you can do this: the first is through physical scrubs, which typically contain tiny particles to manually slough off flakes; the second is through chemical exfoliants that frequently come in liquid forms.
How can you tell? If you see the word "acid" — like salicylic acid, glycolic acid, lactic acid, and polyhydroxy acid — listed on a product, chances are it's a chemical exfoliant.