1. Someone who engages in very frequent or vigorous sex. I've just never really been a sex machine. I prefer spending time with my romantic partners in other ways.
2. Someone who can provide frequent sexual satisfaction to their partner. There's a belief that all women want total sex machines for boyfriends and husbands, but that's simply not true.
n. a sexually promising person; a person obsessed with sex. Heidi looks like such a sex-machine, but she is a real wallflower.