Debrett'sDe‧brett's /dəˈbrets/ (also Debrett) noun 
a book that is a guide to the British royal family and other upper-class families in the UK. It provides information about members of these families, the properties they own, and their history.
a book that is a guide to the British royal family and other upper-class families in the UK. It provides information about members of these families, the properties they own, and their history.