Lookups spiked on August 20, 2014.
The murder of journalist James Foley and the increasing violence perpetrated by ISIS in Iraq and Syria have brought attention to their goal of founding a modern caliphate centered in the territory that they control.
A caliphate is the rule of the entire Islamic world by a single civic and spiritual leader, called a caliph.
The original caliphates grew through expansion and conquest in the centuries following the death of the Prophet Muhammad in A.D. 632. The word comes from the Arabic word meaning "successor," since a caliph was viewed as a successor to Mohammed.