The word is used, in a technical sense, in the Hindu re!igion to denote the descent upon earth of a portion of the essence of a god, which then assumes some coarser material form, be it animal, monster, or man. Such descents are ascribed in the mythology of Hinduism to various gods, but those ascribed to Vishnu are by far the most important. They are believed to have taken place at different ages of the world, and to have consisted of different proportions of the essence of the god Vishnu. Their number is variously stated, ranging from ten to twenty-eight, finally becoming indefinitely numerous. Any remarkable man is liable to be regarded as a more or less perfect avatar of Vishnu, and the consequence one of the worst features of Hinduism - has been the offering of divine homage to men, especially the founders of religious sects and their successors.

In Hinduism, an avatar or avatara, is the incarnation (bodily manifestation) of an Immortal Being, or of the Ultimate Supreme Being. It derives from the Sanskrit word 'avatara' which means "descent" and usually implies a deliberate descent into mortal realms for special purposes. The term is used primarily in Hinduism, for incarnations of Vishnu the Preserver, whom many Hindus worship as God. The Dasavatara (see below) are ten particular "great" incarnations of Vishnu.

Unlike Christianity, and Shaivism, Vaishnavism believes that God takes a special (including human) form whenever there is a decline of righteousness (dharma) and rise of evil. Lord Krishna, an avatar of Vishnu, according to Vaishnavism that is espoused by Ramanuja and Madhva, and God in Gaudiya Vaishnavism, said in the Gita: 'For the protection of the good, for destruction of evil, and for the establishment of righteousness, I come into being from age to age.' (Bhagavad Gita, Chapter 4, verse 8.) In any event, all Hindus believe that there is no difference between worship of Vishnu and His avatars as it all leads to Him.The word has also been used by extension by non-Hindus to refer to the incarnations of God in other religions, notably Christianity, for example Jesus.

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