This is when oral sex of the Fellatio nature is preform and the giver of this sexual act is lacking a substation percentage of his or her teeth and or their teeth are of inadequate size and therefore do not fill an adequate percentage of their mouth; therefore giving the sensation of a completely smooth blow job.
A j-j can also include twins stricken with the affliction above taking turns on receiver of this unique fellatio
Brad - "I totally got a J-J from that girl with no teeth"
