In early Hindu philosophy, turiya (also called caturtha) is a state of Pure Consciousness, or the experience of ultimate reality and truth. It is a fourth state of consciousness that underlies and at the same time transcends three common states of consciousness: (i) the state of waking consciousness, (ii) the state of dreaming, (iii) and dreamless sleep.
The first two states are defective as experiences of reality and truth because of their flawed dualistic natures of subject and object, self and not-self, ego and non-ego. The third state, dreamless sleep, is a type of non-consciousness because it has no subject and object distinctions, and is therefore nearer to the Hindu concept of unity with Brahman, or World Soul. Dreamless sleep is still not complete union with Brahman, however, because in deep dreamless sleep there is no sense of self or the world. Conversely, turiya is the experience of self and world in their pure essences unified with Brahman.
The Mandukya Upanishad defines turiya as follows,
"The fourth state is not that which is conscious of the subjective, nor that which is conscious of the objective, nor that which is conscious of both, nor that which is simple consciousness, nor that which is all-sentient mass, nor that which is all darkness. It is unseen, transcendent, the sole essence of the consciousness of self, the completion of the world."