Hajduk is a term most commonly referring to outlaws, brigands, highwaymen or freedom fighters in Southeastern Europe, and parts of Central and Eastern Europe.
In the Ottoman Empire, the term hajduk was used for Balkan bandits, brigands, while for the South Slavs it was used for bandits who "protected" Christians against perceived Ottoman oppression. In the 17th century, the concept was firmly established in the Ottoman Balkans, related to increased taxes, Christian victories against the Ottomans, and general security decline. Hajduk bands predominantly numbered one hundred men each, with a firm hierarchy under one leader. They targeted Ottoman representatives and rich people, mainly Muslims, for plunder or punishment to oppressive Ottomans, or revenge.
In Balkan folkloric tradition, the hajduk (hajduci or haiduci in the plural) is a romanticised hero figure who steals from, and leads his fighters into battle against, the Ottoman or Habsburg authorities. They are comparable to the English legend of Robin Hood and his merry men, who stole from the rich (which as in the case of the hajduci happened to be also foreign occupants) and gave to the poor, while defying seemingly unjust laws and authority.
In reality, the hajduci of the 17th, 18th and 19th centuries commonly were as much guerrilla fighters against the Ottoman rule as they were bandits and highwaymen who preyed not only on Ottomans and their local representatives, but also on local merchants and travelers. As such, the term could also refer to any robber and carry a negative connotation.
The etymology of the word "hajduk" is unclear. One theory is that hajduk was derived from the Turkish word haidut or haydut, which was originally used by the Ottomans to refer to Hungarian infantry soldiers. Another theory suggests that the word comes from the Hungarian hajtó or "hajdó" (plural hajtók or "hajdók"), meaning a (cattle) drover. Indeed, these two theories do not necessarily contradict each other, as the Balkan word is said to be derived from the Turkish word haiduk or hayduk (bandit).