The Google+ team says that this new feature is called an extra layer of security that ensures only users in a given organization can join. This feature of Google+ gives an ideal tool for groups who want to have social conversations, without broadcasting their thoughts to the world.
Administrators can have the option for the community to be open to everyone or private within their company domain. Once the community is created, users can share files from Google Drive, as well as videos, photos, and events. Community owners/administrators can easily change the moderation of the community or add members to it.