Verified answer

"Mansa is a Mandinka word meaning "king of kings". It is particularly associated with the Keita Dynasty of the Mali Empire, which dominated West Africa from the thirteenth to the fifthteenth century. Powers of the mansa included the right to dispense justice and to monopolize trade, particularly in gold."

-- http://en.wikipedia.org/wiki/Mansa

NOTE: it would have been faster just to google this, instead of asking us.