Similar to a queef. It's the gassy sound that is made when a man pulls his dick out of an anus, of a girl or a guy, during anal intercourse. This sound is not a fart. Rather, it is caused by the combination of K-Y Jelly and air being pushed into the ass during sex.
"So, I was fucking this girl in the ass the other day, and when I pulled my dick out, she let out this massive feef!!"