world of formlessness ［無色界］ ( ārūpya-dhātu; mushiki-kai): Also, realm of formlessness or world of spirit. The highest division of the threefold world. The world of formlessness lies above the world of form and the world of desire. It is the immaterial realm of the spirit, which is said to be free from the limitations of matter and from all thought of matter. This world comprises four realms, which 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 Realm of Neither Thought Nor No Thought is also called the Summit of Being Heaven because it is the highest heaven (summit) in the world of being, i.e., in the threefold world, or the entire realm of existence. The life spans of beings in these four realms are 20,000 kalpas in the first realm, 40,000 kalpas in the second realm, 60,000 kalpas in the third realm, and 80,000 kalpas in the fourth realm. There are four successive levels of meditations called the four meditations on formlessness that respectively lead to rebirth in a successively higher one of these four realms. These realms are also described as states of mind in which one can dwell by achieving the corresponding meditation. The Sanskrit word ārūpya means formless, and dhātu means world or realm.