A galley slave was a slave rowing in a galley, either a convicted criminal sentenced to work at the oar, or a kind of human chattel, sometimes a prisoner of war, assigned to the duty of rowing.

A galley was a type of ship which relied mostly on oars for propulsion that was used for warfare, trade, and piracy mostly in the seas surrounding Europe. It developed in the Mediterranean world during antiquity and continued to exist in various forms until the early 19th century. It typically had a long, slender hull, shallow draft, and often a low freeboard. Most types of galleys also had sails that could be used in favourable winds, but they relied primarily on oars to move independently of winds and currents. The term "galley" originated from a Greek term for a small type of galley and came in use in English from about 1300. It has occasionally been used for unrelated vessels with similar military functions as galley but which were not Mediterranean in origin, such as medieval Scandinavian longships, 16th-century Acehnese ghalis and 18th-century North American gunboats.