A concave area of an Avali between the butt and tail. The area contains fluff and a fur tuft. The area is concave due to side coverings, often made of feathers.

To be given this tag, the Avali pictured must have this part of the body exposed (such as lying down, from a raised tail, or the perspective is a low-angle view), be visibly non-convex (flat underfluffies are fine), and contain fluff of some kind. See also post #1654593 which started the meme of avali underfluffies.

post #1421410