What is Turiya ?
According to Mandukyopanishad - "Turiya, according to the wise, remains unaware of the external, intermediate and internal worlds. He lies beyond both consciousness and unconsciousness; it is indescribable, bearing no relation to anything, where sight cannot penetrate, nor thought. Turiya enjoys pure awareness and experiences peace, bliss and no-duality. He is none other than Atman. Realize Him.
Turiya is a state of mind which one achieves when he is rid of mental impressions and mental bondages of time and space. Mind is just a medium between the cosmic will and self.
Once the mind stops throwing the dust of thoughts, ideas, impressions, memories, and all mental jargon, there is clarity and stillness. Through this clarity one can see and feel the cosmic power. The mind becomes the medium to experience transcendence. This mental state is Turiya.