Русско-англо-русский юридический словарь

The head of state is the highest-ranking constitutional position[note 1] in a sovereign state. The head of state is vested with powers to act as the chief public representative of that state. Heads of state in most countries are natural persons holding an office. In a monarchy the reigning monarch is the head of state, though the title may not be king or queen. In a republic the head of state is usually titled president, but may have other titles such as chairman. (Wikipedia)

Sons and daughters of any future UK monarch will have equal right to the throne, after Commonwealth leaders agreed to change succession laws. (BBC News)

A personal union is the combination of two or more states that have the same monarch while their boundaries, laws, and interests remain distinct. (Wikipedia)

A monarchy is a form of government in which a person, the monarch, is head of state for life or until abdication. The political legitimacy and authority of the monarch may vary from purely symbolic (crowned republic), to restricted (constitutional monarchy), to fully autocratic (absolute monarchy), and can expand across the domains of the executive, legislative and judicial. A monarchy can be a polity through unity, personal union, vassalage or federation, and monarchs can carry various titles such as king, queen, emperor, Raja, khan, caliph, tsar, sultan, or shah. (Wikipedia)