What Does Closed User Group Mean?
A closed user group (CUG) is a group configuration that limits access beyond the defined set of group members. This type of setup can be useful in digital and telecommunications service designs.
Techopedia Explains Closed User Group
Although CUG may be used to refer to an exclusive service that is deliberately closed to benefit its members, most definitions of it involve restrictions that are put on the members themselves. In the telecommunications industry, for example, CUG members can only make and receive calls within the user group. Service providers use a CUG to provide value for cost and to present additional options to customers.