Mysticism is a religion or religious belief based on union or communion with a deity, or divine being. Mysticism is what lets you transcend the physical to experience enlightenment — let's just say you'll recognize it when it happens.
Mystical, mysterious, and filled with wonder, mysticism is easily associated with crystals, New Age theories, or the occult (the supernatural). The truth is that many faiths, including Hinduism, Judaism, and Christianity, have their own forms of mysticism, placing an emphasis on spiritual connection and union, and the mysteries of religion over dogma or rigid rules. Outside of religion, mysticism is applied to cryptic, obscure, or irrational thought — leaning toward mystery and wonder, rather than logic.