In short, it can mean whatever you want it to mean; you have full control over the actual level of "private". Choose whether you'll allow educators to match with projects only from your private marketplace, only from the public open marketplace, or both; choose how you want your portal to appear to the outside world from fully viewable to completely private behind an invite; choose how you enable companies to interact with the portal via open or private marketplaces; choose how you allow learners access to your portal from submitting member requests to invite / import only. The list goes on.