four realms of the world of formlessness ［四無色界・四無色天・四無色処・四空処］ ( shi-mushiki-kai, shi-mushiki-ten, shi-mushiki-sho, or shi-kū-sho): Also, four heavens of the world of formlessness. The four heavens composing the world of formlessness, the highest division of the threefold world. They are said to be realms free from the bonds and limitations of matter and from all thought of matter. The four heavens or realms are, in ascending order of quality, the Realm of Boundless Empty Space, the Realm of Boundless Consciousness, the Realm of Nothingness, and the Realm of Neither Thought Nor No Thought. The practice of meditation leads to rebirth among these four realms; the deeper the meditation, the more superior the realm one attains. The four levels of meditation leading to their respective realms are termed the four meditations on formlessness. Each meditation is named for the realm it leads to, with the first being meditation on the Realm of Boundless Empty Space, the second, meditation on the Realm of Boundless Consciousness, and so on. The Realm of Neither Thought Nor No Thought is also called the Summit of Being Heaven because it is the highest heaven in the threefold world, that is, the highest heaven in the entire realm of being or existence.