Residence card of a family member of a Union citizen
European Economic Area (EEA) citizens have the right of free movement and residence throughout the EEA. This right also extends to certain family members, even if they are not EEA citizens. A Residence card of a family member of a Union citizen is issued to the family member to confirm this right of residence.
Source: Wikipedia — Residence card of a family member of a Union citizen (CC BY-SA 4.0)