When the ass on a girl is so tight and so small that it seems that she is an anorexic. Usually pointed out by tight fitting yoga pants or tight fitting jeans.
Most white actresses and Olympic athletes have this condition, and its sweeping across the nation and infecting every slut in schools everywhere. They wear Abercrombe yoga pants to show off how skinny and white they are.
"Why is Sarah only a size 6 in yoga pants?"
"Its cause she has an anorexic ass and she can fit into it.