From the longer Wikipedia page 
Voivode or Vojvoda (/ˈvɔɪˌvoʊd/; Old Slavic, literally "war-leader" or "warlord") is an Eastern European title that originally denoted the principal commander of a military force. It derives from the word vojevoda, which in early Slavic meant the bellidux, i.e. the military commander of an area, but it usually had a greater meaning. In Byzantine times it referred to mainly military commanders of Slavic populations, especially in the Balkans, first Bulgaria being established as permanent Slavic state in the region. The title voevodas (Greek: βοεβόδας) was first used in the work of the 10th-century Byzantine emperor Constantine VII Porphyrogennetos De Administrando Imperio to identify Hungarian military leaders.
Vojvoda is a title worn in the Middle Ages by a governor of a city or a district in Bulgaria, primarily located in the border territories. The etymology of the word comes from "вой" short for war, and "вода" - a short for “leader”. It was used primarily during wars and was not inherited. The chief military commander of the royal troops was titled the Great Voivode and practically replaces the ruler in the command of the army. Voivoda was one of the four main classes in Bulgaria, namely: voivodes, farmers, craftsmen and traders. After the conquest of Bulgaria by the Ottoman Empire, the title lost its ruling character and was transformed into a title for the most notable participants in the Bulgarian National Liberation Movement, those who were leading a detachment (a battalion, a cheta) in upliftings against the Ottoman rule.
In medieval Serbia it meant a high-ranking official and – before the Ottoman conquest in the 15th century – the commander of a military area. During Ottoman times, voivode was the title borne by the ruler of a province, whose powers included the administration, security and tax collection under a special regime. According to the chronicle of the Voutsas monastery, the Slavic title of "voivode", which prevailed in certain areas of Epirus and Thessaly before the Ottoman conquest, used to denote the leader of a Vlach community or family. The word gradually came to denote the governor of a district.
The territory ruled or administered by a voivode is known in English as a voivodeship. In the English language, the title is often translated as "duke" or "prince". In Central and Eastern European terminology, the rank of a voivode is considered[by whom?] equal of that of a German Herzog. A voivode was considered to be an assistant of the Knyaz. Yet the title could have been used by the Knyaz himself. During military actions the voivode was in charge of a conscripted army that consisted of the local population, the voj (voi); while the knyaz had its own regular military formation, the druzhina.
As of 2016 in Poland the term wojewoda means the centrally-appointed governor of a Polish province or voivodeship (Polish: województwo). The Polish title is sometimes rendered in English as "palatine" or "prince palatine", in charge of a palatinate. Other similar titles include Margrave (Frontier-Governor), Governor-General, and others. With the expansion of the Russian Empire the title of voivode was superseded by namestnik (compared to viceroy). The title was used in medieval Bulgaria, Bohemia, Bosnia, Croatia, Serbia, Macedonia, Greece, Wallachia, Moldavia, Transylvania, Rügen, Lusatia, Poland, Muscovy (later Tsardom of Russia), Halych, Volhynia, Novgorod Republic, Chernigov, and Kiev. Later, voivode denoted the highest military rank in the principalities of Montenegro and Serbia, and in the Kingdom of Yugoslavia.
In the Romanian medieval principalities of Moldavia and Wallachia, "voievode" became part of the official titulature of the sovereign prince, showing his right to lead the entire army. Voivode or vajda (Baida) was also the title of the Hungarian governors of Transylvania in the Middle Ages. Baida was a title of a Ruthenian nobleman and Cossack leader Dmytro Vyshnevetsky. Similarly, the rebel leaders in the Balkans were called "voivodes