What is the relation between caste and religion?

Caste is a social group religion is a belief one is a choice generally the other is not.

Caste and religion are closely related in Hinduism. Hinduism is the world's oldest major religion and is the predominant religion in India. Hinduism is an extremely diverse and complex belief system characterized by a belief in reincarnation. An integral part of Hinduism is its pattern of social classes called a "caste system".