Mysticism: This refers to the pursuit of communion with or conscious awareness of ultimate reality, the divine, spiritual truth, or God through direct experience or insight.
Dervish: A member of a Muslim (specifically Sufi) religious order who has taken vows of poverty and austerity. Dervishes first appeared in the 12th century; they were noted for their wild or ecstatic rituals and were known as dancing, whirling, or howling dervishes according to the practice of their order.
Tariqa: In Sufism this is the term used for a school or order of spirituality. It's like choosing a specific path on your hike towards reaching the peak - that peak being divine love and knowledge.