Shi'a Islam or Shi`ism (from the Arabic word شيعة, short for the historic phrase shi`at `Ali شيعة علي, meaning "the followers of Ali") is the second-largest Islamic denomination. The singular/adjective form of this name is Arabic shi`i شيعي. This is used to refer to a follower of the Ahlul Bayt, and in particular a follower of Ali ibn Abi Talib, who was the Islamic prophet Muhammad's cousin, his son-in-law, and the father of Muhammad's only descendants. Ali was the male head of the Ahlul Bayt (Muhammad's household).