Tax based on one-fifth of the war booty given by Muslims to Muhammad and his family. After Muhammad's death, khums was interpreted as an Islamic tax on profits of various sorts. Most important in Shii Islam. In the thirteenth century khums was split into two portions—one portion went to support indigent descendants of Muhammad, and the other portion went to mujtahids, who were to give half to the imam and half to the poor and orphaned descendants of Muhammad. Gave the Shii clergy in Iran in particular a source of income that granted them independence from the state and helped fuel the Iranian revolution.
See also Taxation