Turiya

Turiya means that which is the fourth. The experiencers (jivas) of the three states of waking, dreaming and deep sleep, known as 'visva', 'taijasa' and 'prajna', who wander successively in these three states, are not the Self. It is with the object of making this clear, namely that the Self is that which is different from them and which is the witness of these states, that it is called the fourth (turiya). When this is known, the three experiencers disappear and the idea that the Self is a witness, that it is the fourth, also disappears. That is why the Self is described as beyond the fourth (turiyatita).

(From 'Spiritual Instruction': IV.8)