Fedayi (Eastern Armenian: Ֆիդայի, romanized: Fidayi; Western Armenian: Ֆէտայի, Fedayi, Turkish: Ermeni milisleri, çeteleri, fedaileri, French: Fédaïs arméniens), also known as the Armenian irregular units, Armenian militia, or Armenian Hayduks were Armenian civilians who voluntarily left their families to form self-defense units and irregular armed-bands in reaction to the mass murder of Armenians and the pillage of Armenian villages by criminals, Turkish and Kurdish gangs, Ottoman forces, and Hamidian guards during the reign of Ottoman sultan Abdul Hamid II in the late 19th and early 20th centuries, known as the Hamidian massacres. Their ultimate goal was always to gain Armenian autonomy (for Armenakans) or independence (for Dashnaks and for Hunchaks)–depending on their ideology and the degree of oppression visited on Armenians.
Some of the key fedayi figures also participated in the Iranian Constitutional Revolution that commenced during the same period, upon agreement of the ARF leaders.