Google Group Types are best described by their underlying permissions and respective use-cases. In general, we have narrowed Google Groups at Appalachian State University down to four individual 'types'.
Public (consolidated from our former types 'Web Forum' and 'Q&A Forum') - Anyone in the organization can post to and join the group.
Team (formerly 'Collaborative Inbox') - Anyone in the organization can post to the group, but individuals must ask to join in order to see messages. Google Group collaborative inbox feature enabled for this group.
Announcement Only (formerly 'Email Distribution Group') - Group owners and managers can post to the group. Organization constituents can join and view all of the group's messages.
Restricted - Group owners, managers, and members can post to the group. Individuals within the organization must be invited in order to join and see messages.
By default, all Google Groups are configured to prevent external users from joining. External users may be allowed by group manager choice.