Original: The Karmapa ( officially His Holiness the Gyalwa Karmapa ) is the head of the Karma Kagyu , the largest sub-school of the Kagyupa ( Tibetan Bka ' brgyud ) , itself one of the four major schools of Tibetan Buddhism .
Simplified: Karmapa is the head of Karma Kagyu - the biggest subschool or lineage of Kagyu school of tibetan Buddhism .