[Celtman]

mean lunch lady:
but what exactly is a caliphate?

      Not exactly exact, but a rough equivalent is "emperor."  Bear in mind that to Islam, separation of church and state just does not compute, so for the shias especially the caliph also has a connotation roughly corresponding to pope. 

      The shias regard the caliphate as hereditary; for the sunnis, the caliphate is elective, and does not depend on heredity.  The last important caliph, the head of the Ottoman empire, was sunni.  For an outline of the Shia and Sunni, see Sunni, Shia, and Sufi Islam. 

[mean lunch lady]

Thanks for the info.