Cadet branch
A cadet branch is the part of a family that is descended from a younger son (or daughter). Cadet branches are important for royal succession since if the main royal branch runs out of people (or out of males, if females are not allowed to inherit the throne), then a cadet branch would inherit the throne. However, sometimes there were also cases where a cadet branch acquired a throne before the main royal branch actually ran out of males, such as when Louis-Philippe of France became French King after Charles X of France abdicated due to the Revolution of 1830 even though Charles X still had a surviving son and grandson of his own during this time.