A 'Demo' (in the context of the Demoscene) is a computer program executing audiovisual effects in real time, as opposed to a movie played on a computer.
The Demoscene is a subculture of programmers, artists, musicians and organizers who create productions, or prods for short.
I'm only interested in demos, a type of prods that are kind of like movies, but for the most part what you see is real-time generated by code that someone spent months perfecting.
The only purpose of demos is to say "Hello everyone, we're still coding and having fun, and this is what we dreamed up just to impress you with our skill and sense of style. Hope you like it, and if you don't, well we're the best! At least much better than you."
It's about bragging rights and experimentation, and the joy of being creative with a computer.
Variants of demos include musicdisks, slideshows, intros, cracktros, megademos and trackmos.
Why don't you join the demoscene and see how far your creativeness and skill can take you? There are competitions, fairs and a huge community who will follow your progress with interest and give you love, respect, and jealousy if you impress them. :)