GroupAdmins are end users who have been promoted by (organization-level) Admins or other GroupAdmins for the purpose of administering users in groups. These special users are generally responsible for adding new users to the group, removing users from the group, changing passwords and editing the various properties of users within the group.
GroupAdmins have less rights than full organization administrators, so are subject to various limitations when administering their groups. The specific rights GroupAdmins enjoy over any particular group are configured on group profiles in the "GroupAdmin Settings" section.
GroupAdmins may also receive notifications about events that happen to the users they have control over, such as password expirations and user lockouts. In order to receive these notifications, GroupAdmin users must have their notifications setting set to "On+Admin". See the Web Interface - Users - Profile page for more information about this setting.