This is a distinct accumulation of fatty tissue on the outer thighs near the buttocks. Usually, when a woman begins to gain weight, the butt wings flare outward. This is not the same thing as fat thighs or a fat ass - it is the area of the anatomy where the buttocks and upper (rear) thighs meet. Butt wings occur on women in their 20s who neglect their bodies (ie. do not exercise or walk regularly) and are more common on American college campuses. Tights and leggings reveal butt wings that jeans or skirts might hide. Butt wings contribute to the pear shape of some women with large hips.
I thought that girl was hot until I noticed her butt wings.
I can't wear polyester pants because they don't hide my butt wings.
Some men anchor themselves into place during cunnilingus by grabbing onto a woman's butt wings.