You can learn more about Drupal, my favourite CMS (content management system) by coming to Toronto's Drupal Day.
So what is Drupal? It's bunch of computer code written in a language called PHP, that lives on a web server (a computer that serves web pages) and delivers websites that are interactive, complex, interesting and/or just plain geeky. For example the federal NDP website uses Drupal, as does The Onion.
While I'm at it, I'll also plug a site I was responsible for: SHARE, an organization worth learning about aside from the coolness of their website. Note that I'm a web development contractor, not a designer - for SHARE, the designer was the fine folks at RaisedEyebrow.
I wish that all sites using Drupal were also of reputable content, or at least not nasty, but there's no technology that can guarantee that.