Refers to a type of scrotum that is loose, long, and fleshy. The ballsac prominently descends, unlike the more average snug sac. This scrotum type can make more of an impression by slapping against a sex partner's chin, anus, etc. Often referred to as a 'set of' referring to the matched pair of balls in a typical nutsac. (It's normal for them to dangle at unequal lengths.)
Look at the set of lowhangers on him! I'd love to roll them around in my mouth and then feel them slapping against my tits when he stands in front of me and fucks my face.
He sat gingerly on the cold bus station bench to avoid traumatizing his lowhangers which were protected only by the thin barrier of his loose nylon running shorts.