Full grain leather is the outermost layer of the bull hide, just blow the fur. It is the most durable form of leather that there is and can last the longest through wear and tear of daily use. Full grain leather is also the most difficult to work with in leather crafting due to it's solidness and thickness.
Full grain leather in it's most natural from is full of nicks, scratches and marks that the animal received from it's natural living habitat. Full-grain leather will also appear to have slight skin wrinkles in some areas where the hide was subject to stretching.