Meta often used as a prefix is a Greek term that means above and beyond indicating a transcendant quality or a raising of the contextual scope of that which is prefixed. In the context of Meta Collab, we use the combination to identify a collaboration of collaborations.
In the case of Meta Collab, meta refers to this wiki's aims of writing about collaboration, collecting theories of collaboration and creating a general theory of collaboration - that is, this wiki's (meta) orientation of being on a conceptual level above the act of collaboration (while engaging in the act itself).
Meta - Meta-Wikimedia, is also quite important to all of Wikia.com (the host of Meta Collab), in that it contains the main version of the MediaWiki Handbook. (MediaWiki is the wiki engine that runs Meta Collab).