The area between and connecting the balls and the shaft of the penis. Also know as "Bottom Lip Dip". The phrases inspiration came from a human specious giving a blow job. When the lower/bottom lip of the human touches that certain area of the males penis which is the end of the shaft and the start of the ball sack.
Man my lower lip dip itches like all get out. I think the girl I fucked last night had crabs.
Dude this hoe last night went lower lip dip like 10 times, I might have to hit her up again.