Mujahideen
Mujahideen (Arabic: المجاهدين) is the plural form of mujahid (Arabic: مجاهد), the term for one engaged in Jihad.
In English usage, it mostly referred to the guerrilla type military outfits led by the Muslim Afghan warriors in the Soviet war in Afghanistan, but now it often refers to other jihadist outfits in various countries.
Early history
In its roots, Mujahideen (an Arabic word) refers to any person performing Jihad. Jihad was the term used for the project of Islamic conquest in the early history of Islam, during the medieval era led by the caliphates (7th through 9th century). In its post-classical meaning, Jihad refers to an act which is spiritually comparable in reward to promoting Islam during the early 600's CE. These acts could be as simple as sharing a considerable amount of your income with the poor and even this definition of Jihad has been exploited by some extremist Muslim groups to include Sexual jihad. Some Islamic sects believe that armed-conflicts cannot be branded as Jihad unless it has been ordered by Messiah.