From The Art and Popular Culture Encyclopedia
A royal family is the extended family of a monarch. Generally, the head of a royal family is a king or queen regnant. The term "imperial family" more appropriately describes the extended family of an emperor or empress regnant, while the terms "ducal family", "grand ducal family" or "princely family" are more appropriate in reference to the relatives of a reigning duke, grand duke, or prince. Finally, it is considered proper in some circles to refer to the extended relations of a deposed monarch and his or her descendants as a royal family.