Ātman (often translated “self”) names the enduring self or conscious principle in many Hindu philosophical traditions. Upaniṣadic teaching investigates the self that cannot simply be reduced to a changing body, passing thoughts, or social identity. This is a philosophical and spiritual claim, not a laboratory-established account of consciousness. The Kaṭha Upaniṣad (1.2.18) is one important traditional locus for the teaching that the self does not perish with the body.
Its meaning is not uniform across schools. Advaita Vedānta understands the deepest ātman as non-different from Brahman. Dvaita Vedānta regards individual selves as real and eternally distinct from the supreme reality while dependent on it. Other schools give distinct accounts of the experiencer, agency and liberation. Therefore “ātman” should be explained with its philosophical context rather than as a doctrine every Hindu school states identically.