ZendUncon 2010 are the Uncon sessions running parallel to ZendCon 2010 (http://joind.in/event/view/459).
The uncon sessions are free stage areas where people can step up as presenter sharing knowledge or continue a discussion from a main-track session. Not only is it a free stage and everyone is welcome.
If you're going to ZendCon, don't forget to pack extra slides for ZendUncon 2010 and step up to become part of the community!