A BarCamp is an ad-hoc gathering born from the desire for people to share and learn in an open environment. It is an intense event with discussions, demos, and interaction from participants. The name BarCamp was inspired as a complement to FooCamp.

I've been to a couple of these, and found all very worthwhile. One was hosted here in San Francisco, at Microsoft's offices. Oddly there was no corporate feel or mandate, just a well-euipt space (projectors esp.) on a weekend, and VERY informal. Granted, the bay area is bit of a hub for such things, but these events are all over the world, regularly. Basically there were about 100 people, it was free, and sessions topics (and room assignments) were created and announced in real time, posted on a big whiteboard. All were free (encourage, even) to move from room to room to find what interests you--i.e vote with your feet. Everybody brought laptops, there was wireless Internet access, and I learned about emerging new ideas that have since become more mainstream.