Refers to the
aesthetic features and overall appearance of someone's posterior. These details can vary widely depending on how a
particular observer views various attributes in the context of
attractiveness/desirability --- where one person may prefer a small firm tight bum as being more ideal for spanking and/or settling on one's lap, someone else might druther a bigger floppier pair of butt-cheeks which are more pleasurable/satisfying to squeeze and knead, especially if the massager himself possesses large hands that he enjoys having "filled".
I don't worry about asspects too much when I date a new lady... to me, if she's got
a sweet placid face and a nice
personality, I could really care less what her butt or tits look like.