Nastika is a Sanskrit term meaning: One who denies; unbeliever. It is the antonym of astika, or one who asserts. The meanings can be generalised respectively into unorthodox and orthodox.

The terms astika and nastika are a traditional classification of Indian schools of thought. Nastika refers to all traditions that reject and deny the scriptural authority of the Vedas. This includes Sikhism, Jainism, Buddhism, the Charvaka materialists and others. Astika refers to those schools that accept the revealed authority of the Vedas as supreme scripture. This includes

In Hinduism, the ninth Avatara of Vishnu was Buddha. Hindus believe that Buddha led a race of pious, noble and realized people who were relieved from the clutches of pantheistic cults existing in those times, people who had gone astray from monist view of thoughts. But a large section of Hindus, particulary the priestly class i.e Brahmins continued to practice their demonic rituals and thereby misleading the fallible and innocent, mitigating the progress of humanity to higher spirutual goals.