The major two school of thoughts within Islam = Sunni (majority), Shia (minority).
Now within these two main schools are various branches for example, Sunnis have Ahmedis, Hanbalis, Salafis etc. Whereas Shias have Agha Khanis, Ismaelis, Zaydis, Alawis etc.
Now, large majority within the Shia school of thought (close to 90%) follows the unbroken chain of the 12 Imams from the lineage of Imam Ali (as) and Fatima (as) (they are also known as Itha Ashari). Within this branch there exists a subgroup that do not approve to follow anybody until the 12th Imam, Al Mahdi (as), returns. This group is known as Akhbari, i.e. they seek guidance exclusively from the Akhbar or knowledge left behind by the 12 Imams. They are mainly found in a certain part of Iraq that I am forgetting the name of at the moment.
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