When one gets fucked from the back whilst bent over giving the other male a blowjob felatio. A girl, (or boy depending) is bent over. Two males are on either side of this person. On one end, a male is fucking a girl in the vagina or ass, while she gives the male on the other side a blowjob. During all of this, they push the girls body back and forth so she has to expell no effort. So, its like a dirty threesome.
"Dude, me and Kyle totally monged her the other night"
"The one with the drawn on eyebrows?"
"Yeah, wanna mong?"