Heterodoxy in a religious sense means "any opinions or doctrines at variance with an official or orthodox position". Under this definition, heterodoxy is similar to unorthodoxy, while the adjective "heterodox" could be applied to a dissident.

Heterodoxy is also an ecclesiastical term of art, defined in various ways by different religions and churches. For example, in the Apostolic Churches (the Orthodox Church, the Roman Catholic Church, the Church of the East, and the Non-Chalcedonian or Oriental Churches), heterodoxy may describe beliefs that differ from strictly orthodox views, but that fall short either of formal or of material heresy.

The three heterodox schools of Indian thought are Carvaka, Buddhism and Jainism. The time of origin of the first cannot be fixed exactly as no early Carvaka works are extant. According to some authorities the Carvaka School had developed before Buddha. Brihaspati is accepted by some as the founder and Carvaka his chief disciple. Others say that Carvaka is the name of the originator. Still a third claim is that Carvaka is not the name of a person but a word signifying pleasure. As to why Carvakism came into being Chandradhar Sharma writes that:

"It must have arisen as a protest against the excessive monkdom of the Brahmana priests. The externals of ritualism which ignored the substance and emphasized the shadow, the idealism of the Upanishads unsuited to the commoners, the political and the social crises rampant in that age, the exploitation of the masses by the petty rulers, monks and the wealthy class, the lust and greed and petty dissensions in an unstable society paved the way for the rise of materialism in India in the post-Upanishadic and pre-Buddhistic age."

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