similar to the common vaginal "fart" or "queef"... BUT (no pun intended) is different in the fact that it is expelled from the anus rather than the vagina.
Timmy pulled his cock out of Johnny's ass and was surprised by the expulsion of air between Timmy's cheeks...
"I swear it wasn't a fart, it was just a buqueef."
While playing the fast-paced action video game, Halo Reach, Carlos failed to score the game-winning frag for his team, as he was distracted by Todd's pestilent buttqueef.