Dream-time was, in the philosophical belief systems of the ancient aborigines of Australia, a kind of parallel timeline, or "time out of time," which coexisted with the objective world. The Dream-time was the realm of spirit beings, and of dreams. Mortals accessed the Dream-time through the Singing.
By the end of the 20th century, only a small number of Australian natives maintained belief in the Dream-time. In time, these individuals learned to integrate their beliefs into the modern world, and by the mid 23rd century, it was considered as legitimate as any other theology.
In 2284, Admiral James T. Kirk sought out Dr. Galarrwuy Nayingul regarding his vivid dreams about the events in the book Strangers from the Sky. Nayingul offered Dream-time as a possible option for understanding his dreams. Kirk agreed, though ultimately he found no answers to his concerns. (TOS novel: Strangers from the Sky)