three realms

(Sanskrit, tridhātu). The hierarchical structure of a universe or ‘world-system’ according to Buddhist cosmology, comprising the Desire Realm (kāma-dhātu), the Form Realm (rūpa-dhātu), and the Formless Realm (ārūpya-dhātu). Also known by the alternative designation of the ‘three worlds’ (triloka).

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

Three Realms  三界  Sanskrit word is Trailokya. It is Buddhist metaphysical equivalence for the triple world of earth, atmosphere and heaven.   1.Realm of Sensusous Desire (Sanskrit word is Kamadhātu) of sex and food. It includes the Six Hevens of Desire, the Human World and the Hells.   2.Realm of Form (Sanskrit word is Rūpaadhātu) of matter which is substantial and resistant. It includes the Heavens of Four Zen (Sanskrit word is Brahmalokas).   3.Realm of Formlessness (Sanskrit word is ARūpadhātu) of pure spirit, where there are no bodies and matters to which human terms would apply, but where the mind dwells in mystic contemplation; its extent is indefinable, but it is conceived of in Four Stages/Places of Emptiness in the immaterial world.

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