(1) The period after an erection in which a man's member/phallus is semi-turgid and not quite yet flaccid. Generally, the penis is accompanied by one or more slightly visible veins.
(2) Double entendre (bone=sex): The ten minute period after a ejaculation/intercourse/masturbation session.
Dustin: Wow, you've got kind of a bulge goin' on down there Andy!
Andy: Yeah bro, I was just in my dorm room with this chick named Tatiana. I'm fresh off the bone!