The imam is a recognized religious leader or teacher in Islam.
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.
The Ismailis trace a different line of Imams, branching at one of Husayn's descendants from the 12-Imam line.