Unprivileged
The group Unprivileged is one of the three groups for which RT manages the membership automatically. The other two are Privileged and Everyone. Every user is either a member of the Privileged group or of the Unprivileged group.
Unchecking the checkbox 'Let this user be granted rights (Privileged)' checkbox on the user administration page makes a user Unprivileged. In a default RT configuration, new users are created Unprivileged, as when an email comes in and a new user account is automatically created.
Unprivileged users get access to the SelfService interface, which is limited to pages under /SelfService/.