The bottom of a book; the part of the book you see when it is lying flat on a table.
I really wish they'd prop the books up so I don't have to look at book asses.
1. To make great haste
2. To walk or run quickly as if you're late for something or you have to use the bathroom
3. A method used when running from authority figures
Origin: a combination of "book it" and "haul ass"
Also, booking ass, and less commonly book assing.
1. "Put on those rollerblades and just book ass down that hall!"
2. "Oh man! It's it good thing I booked ass or I would've been late to class!"
3. "The cops saw us doing recreational drugs. That's about when we booked ass"