Interest Groups are public groups that Content Glass users can use for sharing widgets of specific interest with other users.
Unlike with private sharing of widgets, interest-group does not require two users to be in a contact or relation. Instead, users that join the group are able to share with each other publiclly.
Accordingly these groups may be subject to admin regulation for example to prevent spamming or adding irrelevant content by participants.
But the most important is that participants of the group will share meaningful information, that is truly related with the subject for which group has been created.