A person who is under a set age. "Underage User" may be used for forums, online games ect... Anywhere online where there is a set age you must be.
Ex.
Bobby is 12. Bobby joins a 13+ forum. Mandy who is 14 and a staff member finds out- Mandy banns Bobby's arse =) and did it because he was a Underage User
the best thing in the world, probably before porn(for most people)
and a great way to waste time with your 'significant other'.
both participants must be under 18 or so of age.(depends on where you live)
two 15 year olds. fucking in the school toilet like rabbits in between classes then skiving off classes just to screw each other. THAT, my friend, is totally underage sex.
Usually a twixter, above legal drinking age, who buys beer for underage kids in return for admission to their parties. First mentioned in a Saturday Night Live Skit.