There is a common misconception that all leather is made equally and genuine leather just means that it is not fake. While genuine leather is real leather, it is only one of four grades in quality.
This is the top layer of the hide, found just below the fur. This is where the grain is the tightest, making it the strongest, most durable part of the hide. This portion of the hide resists moister very well and over time develops a stunning natural luster from use.
Top Grain Leather
This leather is similar to Full Grain leather. The difference it that is it not quite as strong and has been sanded and buffed, removing a few millimeters off the top to reduce any scratches or imperfects from the surface. This gives the leather a more uniform look with less of the scars and scratches that occur naturally. Often there is a finish coat added which reducing the leathers breath-ability but has a greater resistant to stains.
This is the portion that remains after the top is split off for the higher grades. The grains are not nearly as tight in this leather. Often artificial grain and patterns are applied to its surface, being treated with stains or dyes to get the desired finish.
This is the lowest quality leather you can get. It is not stripped from the hide but bonded (glued) pieces of dust and shavings pressed together. Essentially it is left over bits and scraps stuck together then resurfaced to create something similar to vinyl.
When purchasing items you still need to be careful. A tactic to selling some products is to state that the item is made with leather, but not all pieces need to be leather to make this statement. Some pieces of the item could be vinyl, having been treated to look similar to the leather portions.