The Imam is a recognized religious leader or teacher in Islam. The term includes the leader of Muslim congregational prayers.
According to the Twelve-Imam Shiite dogma, imam refers only to one of twelve early leaders of Islam—Ali, Hasan, Husayn, and nine of Husayn's descendants. See: Shia Imam
The Ismailis trace a different line of Imams, branching at one of Husayn's descendants, Ismail bin Jafar.
The Zayidis trade a different line, branching at Husayn's grandson.
Sunnis accord the title to the greatest Islamic scholars.