There are several synonyms for the term "Shiite Muslim" which is a branch of Islam primarily practiced in Iran, Iraq, Bahrain, and Lebanon. Some of the common synonyms for Shiite Muslims are Shia Islam, Shiism, Shi'ite, Shi'ism, and Shiite Muslimism. The term Shi'ite derives from the phrase Shi'atu Ali which means "followers of Ali." Shiites believe that Ali, the son-in-law of Prophet Muhammad, should have been the first caliph instead of Abu Bakr. Shiite Muslims are known for their distinctive religious practices such as mourning rituals during Muharram and the celebration of Ashura.