fanny fallout 

When an extremely slender woman has legs that do not touch at the thighs when she walks or stands naturally. As her legs don't touch, you can clearly see the shape of her vagina between said thighs, the outline revealed for all to see. Considered desirable amongst women.

Girl #1: Eww! I can see the shape of her fanny because she's so skinny!
Girl #2: Are you kidding? I wish I had fanny fallout.
Dude: Damn, that's fine!

fanny fallout by truereligion25 April 29, 2010

fanny fallout 

When a woman's thighs don't touch, creating a subtle bulge in the crutch where the vagina is.

Girl: Holy shit, Sarah's so skinny she has fanny fallout!
Guy: I love it when chicks legs are that skinny!

fanny fallout by flowerpots February 17, 2010