The 'Orphaned Users' group was added in version v5.2.3.R20100826 of Shout. All contacts need to belong to at least one group. Otherwise the data about the contact becomes hidden although it still exists in the database. The Orphaned Users group was added as a way for the administrator to view the hidden contacts and decide what to do with them (delete them or add them to other groups).
There are a number of ways that contacts can become orphaned such as deleting a group containing contacts, adding a contact through a form which does not have a group to associate the individual to, and adding a contact in the administrative console without assigning a group.
Code changes have been implemented throughout the various upgrades to mitigate the risk of most of these situations, so the Orphaned Users group is, for the most part, legacy information.
