The frozen frame is a subset of the snapshot that comprises all statistical units that are active, or potentially active, or active within the previous reference year. It also includes administrative units that are linked to these statistical units. The aim is to include all units and all characteristics that are used by subsequent processes. In other words it is a trimmed down version of the snapshot that is easier to manipulate because the possible large number of inactive units are not there. It may be further restricted by containing only units for which there are values for the characteristics that are to be used for frame extraction and sample selection for at least one survey.