Ātman Skt.; according to the Hindu understanding, the real immortal self of human beings, known in the West as the soul. It is the nonparticipating witness of the jīva, beyond body and thought and, as absolute consciousness, identical with brahman. Philosophically atman is known as kūtastha. In virtue of its identity with brahman, its special characteristic marks (ātmakara) are identical with those of brahman: eternal, absolute being; absolute consciousness; and absolute bliss.
In Buddhism the existence of an ātman is denied: neither within nor outside of physical and mental manifestations is there anything that could be designated as an independent, imperishable essence. (Also anātman, skandha.)
Source: The Encyclopedia of Eastern Philosophy and Religion: Buddhism, Hinduism, Taoism, Zen. Shambhala Publications, Inc.
External link: Ātman (Buddhism) / Ātman (Hinduism)