A demo, for me, is showing off various techniques usually based on a theme. For example a few years back there a were a few Lord of Rings or Blade themed demo contests. So contestants basically had to write a demo that revolved around those themes. Demos are usually self running and often loop, and the only user interaction is to press the ESC key to shut down.

Have a look at this demo ( http://www.sulaco.co.za/nitrogen/fil.../Foundry13.zip ) to get an idea of what I mean. This demo was themed on Earth, Water, Fire and Air. Actually there is a post mortem of the demo available @ http://www.sulaco.co.za/nitrogen/projects.html and also source if anyone is interested.

PS. Guys please supply a feature list for your games .