If you're referring to the white 'cracks', I've read that it can be the result of Vitamin A deficiency. (Depends on how deep the cracks are - if they're bad, then have a chat with the avian vet for dietary requirements)
Otherwise, if its the white edging where the skin meets the beak, I think it's the same as the little flap of skin we have at the base of our nails/cuticles. I could be wrong though. Why not ask your avian vet next time you're in there for a checkup?