The four states of consciousness are jagrat, svapna, shushupti and turiya. Jagrat is waking consciousness, svapna is the dream consciousness, shushupti is the deep sleep consciousness and turiya is higher consciousness which is beyond all previous states.
Entering the state of turiya requires inner silence. It can be achieved when the mind is free of mental blocks and bondages with time and space.
The goal of yoga and meditation is to achieve turiya, where oneness is felt with the universe.