An unconference is a conference where the content of the meeting is driven and created by the particpants rather than by a single organizer. Barcamp is a series of UnConferences, sharing the same name and format. Barcamp is a bottom up approach rather than a top down approach of organizing a conference. It's a common a place for techie's to hang out and geek out- and share knowledge and experiences.
While it seems to be getting a renewed push this past year with BarCamps and Blogger driven conferences, the concept and the term (UnConference) itself was used as early as 1998 in this XML COnference. The present day UnConferences, in its incarnation as BarCamps follow a simple format, where there are no pure spectators, and everyone at the event particpates- either present, give a demo or help with a demo/ppt, actively discuss. And, while the theme s decided and publicized, most speaker slots are taken up adhoc on the day of the event.
Very interesting. Even more so if you look at some parallels with the Web2.0 architecture. The Unconferencee movement (now) is fuelled by bloggers, and the unstructured information/knowledge share phenomenon that is fuelled by the blogs, TSS feeds and such over the internet. Not too different from how Web 2.0 is emerging as a new software first mile (user end) architecture that uses web and its sites/services as the infrastructure to provide an end user solution. The whole Web 2.0 is semi-structured. The structure exists only in the end application. The "providers" of the various components such as blogs, sites, services, SOA et al just "provide", without knowing exactly who or how of the consuming end in the Web 2.0 scheme of things.
The unconference draws some parallels to Web 2.0. It is semi-structured. Adhoc. Everyone participates. Anyone could listen or speak. Much like Web 2.0 where anyone could "provide" or "consume". A fairly unstructured with a bunch of good-practices rather than rigid rules.