1. To be very sexually attractive or exciting. Man, that supermodel is really hot stuff!

2. To be particularly popular, fashionable, interesting, exciting, etc. That new talking robotic doll is hot stuff for gift-seeking parents this holiday season. That new pilot thinks he's hot stuff, but he's got a lot to learn.

3. Especially of media (such as books, magazines, videos, etc.), to be erotic or salacious. Man, this magazine you swiped from your brother's room is hot stuff!