The starting point is Michael Warner, "Publics and Counterpublics, pdf 
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Here's a summary: Publics are self-organized spaces organized by discourse. They are impersonal, and an organization of strangers. What holds a public together is that it is addressed as a public. That is, what constitutes a public is attention. It's where discourse circulates, and is circulated by. It's made of links. Publics come and go: they are located. And a public calls into existence the world it exists in. Warner writers that "a public is poetic world making." I prefer that a public is heuristic. My emphasis stays on the discourse. Warner's moves towards agent action and interaction.
Why is Warner's idea of a public valuable in thinking about Fedwiki?
as a counterpoint or even escape from _community_
the emphasis is on publics as generative, and the concept seeks to consider how publics are generated, evolve, disband
the term _pubic_ more accurately describes the position of Fedwiki users, both empirically and epistemically, than does _community_.
the term keeps the emphasis on the discourse and how it links agents, keeps a focus on the agency of attention, discourse creation, and circulation. _Community_ keeps sliding into social agency.
other
a pretty good summary of Warner's major book, _Publics and Counterpublics: webpage