The Shia meaning "followers", "faction" or "party" of Muhammad's son-in-law and cousin Ali, whom the Shia believe to be Muhammad's successor in the Caliphate. Twelver Shia (Ithnā'ashariyyah) is the largest branch of Shia Islam and the term Shia Muslim is often taken to refer to Twelvers by default. Shia Muslims constitute 10–20% of the world's Muslim population and 38% of the Middle East's entire population.
