Tiered Cosmos – Among some, but far from all, societies that employ shamans, the cosmos is understood to be layered, often in three levels: an upper world, middle world, and underworld. Ordinary humans live entirely in the middle world, unless their souls are taken by otherworld persons or spirits. Shamans work in all three worlds, mediating between their communities and other-than-human persons of many kinds, including animals. Neo-shamans often conceive of these other worlds as inner (psychological) and imaginal realms requiring Jungian-style therapeutic and individuated interpretations.
SOURCE:
Historical Dictionary of Shamanism by Graham Harvey and Robert J. Wallis 2007