The act of performing cunnilingus on a girl by pulling the female's vaginal lips apart, then shaking your head violently and fully relaxing your cheeks and lips. Also, a sound effect like you are really going to town and getting dirty with this girl's vagina is welcome, and is almost 100% necessary for the woman's full satisfaction. Any saliva that falls out of your mouth while doing so is just added lubrication. Based from the character Boss Nass in Star Wars.
Dude, I just boss nassed that girl last night! She came within five seconds!