Tsar (/zɑːr, sɑːr/ or /tsɑːr/; Old Church Slavonic: ц︢рь [usually written thus with a title] or цар, царь), also spelled csar, or tzar or czar, is a title used to designate East and South Slavic monarchs or supreme rulers of Eastern Europe, originally Bulgarian monarchs from 10th century onwards.
As a system of government in the Tsardom of Russia and the Russian Empire, it is known as Tsarist autocracy, or Tsarism.
The term is derived from the Latin word Caesar, which was intended to mean “Emperor” in the European medieval sense of the term—a ruler with the same rank as a Roman emperor, holding it by the approval of another emperor or a supreme ecclesiastical official (the Pope or the Ecumenical Patriarch)—but was usually considered by western Europeans to be equivalent to king, or to be somewhat in between a royal and imperial rank.
Tsarist autocracy[a] (Russian: царское самодержавие, transcr. tsarskoye samoderzhaviye) is a form of autocracy (later absolute monarchy) specific to the Grand Duchy of Moscow, which later became Tsardom of Russia and the Russian Empire.[b] In it, all power and wealth is controlled (and distributed) by the Tsar. They had more power than constitutional monarchs, who are usually vested by law and counterbalanced by a legislative authority; they even had more authority on religious issues compared to Western monarchs. In Russia, it originated during the time of Ivan III (1440−1505), and was abolished after the Russian Revolution of 1917.
West Europeans have had Kings, and Constitutional Monarchies but they were limited by traditional (customary) law.