An Ass Smile is a very common attribute of ass on regular asses, more common to see than the completely and the more spectacular Apple Bottom, or the ghetto crowd favorite Ghetto Blasters. The Ass Smile is not a class of ass, rather it's a section of the ass that is necessary in all nice looking asses. This is what white boys used to refer to when they said they liked a 'heart shaped ass'. They're talking about the way the booty meat is defined well (most likely in the bottommost/innermost sections of booty meat), separating the cheeks well. The Ass Smile will dress up an ass and save it from looking completely disgusting, in many cases. When someone has a nice Ass Smile, but a terrible looking ass, overall, a photographer, or themselves, might bend the model over so you can see the UNDER-ASS, where the Ass Smile exists. This is to hide the fact that rest of the ass is disgusting and flat, fat or non-existent. You see pics where girls look like they have nice juicy asses, but if you look close, they've not tops to their asses- nor is it sloped-, have long flat backs/asses, but the bottom is so wonderfully rounded off that you can't dismiss that ass completely. This kind of ass normally wears panties with a large backside material to hide the long lower back and also panties that have rounded cuts to the legs parts, so that the Ass Smile can get accented by the panties rounding it off. If a really flat assed chick has an Ass Smile, many guys say that's a really nice ass. So it's the SAVIOR of asses! The Ass Smile is that definition of ass meat, as the ass rounds off into the legs- accompanies by ass crease that extends. A good Ass Smile clearly separates the ass from the thighs. If this is not present, there is no Ass Smile on a chick and her back looks like it goes right into the legs!" http://www.assmatrix.com/types.htm