any surface at around ass level that serves as a make shift seat. Common types of ass shelves are window sills, arms of chairs, any sort of ledge, and if your creative your friends. As the word "shelf" suggests in the term, ass shelves serve as the perfect place to store your ass when a regular chair just won't do the trick.

Got the covid-19 vaccine

Part of a woman's body just below the small of the back that curves out to form the top of her ass.

A massive ass that seems detached from the rest of the body and could easily be used as a table.