The word comes from the Greek myein, to close the eyes or lips, and mystikos, “hidden”, first used of the secret rites of the mystery religions and then of the hidden sense of scripture. In modern usage it names the experiential core of the religions: the knowledge of God, the Self or the Real that is had by union rather than by report.
Mysticism
The pursuit and experience of direct, transforming union with, or knowledge of, ultimate reality.
Also: mystical tradition