The patch of hair that appears between a males balls and a-hole (taint). Generally sweaty, motley, and congregates itself as a lock of hair, thus a "sweaty motlock".
Also known as: Taint hair, Tainthawk, Ball Mullet,
........ "Hey man, whats with that sweaty patch of hair between your balls and your ass?" "Why are you looking at my balls? It's my Sweaty Motlock."