Monarchs, as such, bear a variety of titles – king or queen, prince or princess (e.g., Sovereign Prince of Monaco), emperor or empress (e.g., Emperor of China, Emperor of Ethiopia, Emperor of Japan, Emperor of India), archduke, duke or grand duke (e.g., Grand Duke of Luxembourg), emir (e.g., Emir of Qatar) or sultan (e.g., Sultan of Oman). Prince is sometimes used as a generic term to refer to any monarch regardless of title, especially in older texts.
A king can also be a queen's husband and a queen can be a king's wife. If both of the couple reign, neither person is generally considered to be a consort.
Monarchy is political or sociocultural in nature, and is generally (but not always) associated with hereditary rule. Most monarchs, both historically and in the present day, have been born and brought up within a royal family (whose rule over a period of time is referred to as a dynasty) and trained for future duties. Different systems of succession have been used, such as proximity of blood (male preference or absolute), primogeniture, agnatic seniority, Salic law, etc. While traditionally most monarchs have been male, female monarchs have also ruled, and the term queen regnant refers to a ruling monarch, as distinct from a queen consort, the wife of a reigning king.
Some monarchies are non-hereditary. In an elective monarchy, the monarch is elected but otherwise serves as any other monarch. Historical examples of elective monarchy include the Holy Roman Emperors (chosen by prince-electors, but often coming from the same dynasty) and the free election of kings of the Polish–Lithuanian Commonwealth. Modern examples include the Yang di-Pertuan Agong of Malaysia, who is appointed by the Conference of Rulers every five years or after the king's death, and the pope of the Roman Catholic Church, who serves as sovereign of the Vatican City State and is elected to a life term by the College of Cardinals.
In recent centuries, many states have abolished the monarchy and become republics (however see, e.g., United Arab Emirates). Advocacy of government by a republic is called republicanism, while advocacy of monarchy is called monarchism. A principal advantage of hereditary monarchy is the immediate continuity of national leadership, as illustrated in the classic phrase "The [old] King is dead. Long live the [new] King!". In cases where the monarch serves mostly as a ceremonial figure (e.g. most modern constitutional monarchies) real leadership does not depend on the monarch.
A form of government may in fact be hereditary without being considered monarchy, such as a family dictatorship.