Seth Godin defines a "tribe" as: "a group of people connected to one another, connected to a leader, and connected to an idea. A group needs only two things to be a tribe: a shared interest and a way to communicate."
One my favorite tribes is The Order of the Fez. A short bus full men who like to wear fezzes. We communicate via blog and email. The notion of a "leader" is somewhat antithetical to fezorocity (our defining Force), but since I maintain the blog I perform that role as needed. More of a recording secretary.
This weekend two of our members sent a music video that nicely captures what the OOTF is about.