Mahdi n. : Among Mohammedans, the last imam or leader of the faithful. The Sunni, the largest sect of the Mohammedans, believe that he is yet to appear.

Example:
What do you know about the Mahdi (Mehdi) Army and their head, Muqtada Al Sadr?

Taxonomy
Mahdi, Islam, Sunni, Imam Mahdi, Al Mahdi, belief, Muslims, Hadith, claim, Muhammad, Imam, Moojan Momen, Shia, scholar, Shi'i, second coming of Jesus, Muhammad ibn, free encyclopedia.

Defination from the web:
Mahdi will be a descendant of Muhammad of the line of Fatimah. His name will be as the name of Muhammad. ... A star with a luminous tail will rise from the East before the Mahdi emerges. He will restore faith to its original form and eradicate moral corruption. ...