"King" designates a male monarch (when he does not use another title such as emperor or tsar). In some countries in Europe, Asia, Africa, North America and the Pacific, a "King" is the hereditary head of a nation-state, except when a queen or other head of state fills the role.
In China, "king" is the usual translation for the term wang, which designated the sovereign before the Qin dynasty and during the Ten Kingdoms period. During the early Han dynasty, China had a number of small kingdoms, each about the size of a county and subordinate to the Emperor of China.
A state ruled by a monarch is called a monarchy.
Few monarchs today exercise absolute authority. Although there are a number of hereditary monarchies still existing in the world, many countries with hereditary royalty are de facto ruled by a democratically elected leader such as a prime minister, while the monarchy continues to hold a symbolic or ceremonial position (eg. United Kingdom; see also constitutional monarchy).
In a few cases a monarch is associated with a particular group (or nation) within a state, such as Te Arikuini Te Atairangikaahu of the Maori[?] (the Maori Queen[?]) and Osei Tutu II of the Ashanti[?]. Malaysia provides an example of a monarch-rich state.
The system for succession to the throne varies from monarchy to monarchy. Traditionally, succession to the eldest son of the monarch has been most common; if the monarch had no sons, the throne would pass either to the eldest daughter, or to the nearest male relative, depending on whether the monarchy accepted female rulers and/or descent in the female line. Some monarchies have abolished this preference for males, and the eldest child of the monarch ascends to the throne, be that child male or female, e.g. some European monarchies such as Sweden.
In some monarchies, e.g. Saudi Arabia, succession to the throne has passed to the monarch's next eldest brother, and only to the monarch's children after that. In some other monarchies, the monarch chooses who will be his successor, who need not necessarily be his eldest son, e.g. Jordan.
See also: dauphin, regent, queen consort