Titular nation
The titular nation is the single dominant ethnic group in the state, typically after which the state was named. The term was used for the first time by Maurice Barrès in the late 19th century.
Soviet Union
The notion was used in the Soviet Union to denote nations that give rise to titles of autonomous entities within the union: Soviet republics, autonomous republics, autonomous regions, etc., such as Byelorussian SSR for Belarusians.
For an ethnos to become titular nation, it had to satisfy certain criteria in terms of the amount of population and compactness of its settlement. The language of a titular nation was declared an additional (after Russian) official language of the corresponding administrative unit.
The notion worked well for the cases of well established, homogeneous and relatively developed nations.
In a number of cases, in certain highly multiethnic regions, such as North Caucasus, the notion of titular nation introduced intrinsic inequality between titular and non-titular nations, especially since the introduction of the "korenizatsiya" politics, according to which representatives of a titular nation were promoted to management position.
China
The People's Republic of China government has adopted some of the principles behind this Soviet concept in its ethnic minority policy. See Autonomous entities of China.