三界 (Jpn san-gai )
The world of unenlightened beings who transmigrate within the six paths (from hell through the realm of heavenly beings). The threefold world consists of, in ascending order, the world of desire, the world of form, and the world of formlessness:
(1) The world of desire comprises the four evil paths (the realms of hell, hungry spirits, animals, and asuras ), the four continents surrounding Mount Sumeru (that contain the realm of human beings), and the first six divisions of heaven (the lowest part of the realm of heavenly beings). The beings in this world are ruled by various cravings, such as those for food, drink, and sex.
(2) The world of form consists of the four meditation heavens, which are further divided into eighteen heavens (sixteen or seventeen according to other explanations). The beings here are free from desires, cravings, and appetites, but still have physical form and thus are subject to certain material restrictions.
(3) The world of formlessness comprises the four realms of Boundless Empty Space, Boundless Consciousness, Nothingness, and Neither Thought Nor No Thought. Here beings are free from desires and from physical form with its material restrictions.