Contact Groups are sub-groups of officials in your organization that can be used for emailing, scheduling, reporting, and more. You can create as many contact groups as you'd like, and users can be present in multiple groups. You can then send messages to these groups (or use them when scheduling, if you're a scheduler too).
Contact Group Permissions
By default, a Contact Group is only visible and usable by the user that created the Contact Group. If the creator wants to share the group with other users to see or edit, they will need to use the permissions settings in the group to change who is allowed to view or edit the group.