Mysticism (from the Greek μυστικός (mystikos) "an initiate" (of the Eleusinian Mysteries, μυστήρια (mysteria) meaning "initiation")) is the pursuit of achieving communion or identity with, or conscious awareness of, ultimate reality, the divine, spiritual truth, or God through direct experience, intuition, or insight. Traditions may include a belief in the literal existence of dimensional realities beyond empirical perception, or a belief that a true human perception of the world transcends logical reasoning or intellectual comprehension. A person delving in these areas may be called a Mystic.
In many cases, the purpose of mysticism and mystical disciplines such as meditation is to reach a state of return or re-integration to Godhead. A common theme in mysticism is that the mystic and all of reality are One. The purpose of mystical practices is to achieve that oneness in experience, to transcend limited identity and re-identify with the all that is. The state of oneness has many names depending on the mystical system: The Birth of the Spirit, the Third Awakening, Illumination, Union (Christianity), Irfan (Islam), Reintegration, Nirvana (Buddhism), Moksha (Jainism), Samadhi (Hinduism), to name a few.
The term "mysticism" is often used to refer to beliefs which go beyond the purely exoteric practices of mainstream religions, while still being related to or based in a mainstream religious doctrine. For example, Kabbalah is a significant mystical movement within Judaism, and Sufism is a significant mystical movement within Islam. Gnosticism refers to various mystical sects which arose out of Christianity. Some have argued that Christianity itself was a mystical sect that arose out of Judaism. Non-traditional knowledge and ritual are considered as Esotericism, for example Buddhism's Vajrayana. Vedanta, the Naths (North India), the Natha (South India), Siddhar, Nagas are considered the several mystical branches of Hinduism. Hinduism being an ancient religion and a rather broad 'all-paths' embracing philosophy has many mystical branches.
Mystical doctrines may reference religious texts that are non-canonical, as well as more mainstream canon (Christian example of the former, Dark Night of the Soul, and the latter Book of Revelation), and generally require a more committed intellectual, psychological and physical approach from spiritual devotees. Most mystical teachers typically have some history or connection with a mainstream religious branch—controversial or otherwise, but gather followers through reinterpreting sacred texts or developing new spiritual approaches from their own unique experience.