This is the final liberated-while-living (Jeevan Mukta) stage of a Yogi or Jnani. In this stage, the body can't be maintained for more than 21 days. A modern example of a Yogi who achieved this stage is Yogananda, whose body did not deteriorate for 21 days after he was clinically declared dead by doctors, here in America.

The title given to the Yogi or Jnani who is in Turyaga stage is "Brahmavid-Varishtha." Here, the Yogi dwells in "Turyavastha", which is beyond the normal states of "Jagrata", "Swapna", and Sushupti; or waking, dream, and deep-sleep states. For our purposes of comprehension, we can translate "Turyavastha" as the "super-conscious" state (as opposed to waking to be conscious, dream to be sub-conscious, and deep sleep to be unconscious states).