Top Grain: During the tanning process leather hides are split into layers. The top layer is referred to as top grain leather. This is the most sought after, softest, and most durable part of the hide due to the strength of its fibers.

Split Grain: A subsequent layer of leather

Protected/Aniline Plus Leather: A leather that has first been aniline dyed throughout and then treated with a secondary dye. The most resistant to stains, scratches, body oils, and heavy use. Perfect for families and other higher use settings. 

Semi Protected/Semi Aniline:  A leather that has first been aniline dyed throughout and then  engineered to posses a mix of natural beauty, softness, and durability.  Often a wax, oil, or secondary dye is applied to give this this leather distressed look or two tone effect.

Untreated/Full Aniline: A leather that is only aniline dyed. The most natural, soft, and unique leather. 

Full Grain: Another term for full aniline.  Top grain leather that is only aniline dyed