Spirits are discorporate entities that are present individually in all parts of nature – animals, plants, rocks, winds, fire, soil, waters, and so on. The Brithini classify them as an incorporeal but ubiquitous, not-quantifable energy present individually in all things and natural forces.
Everything has a spirit, often several. Spirits inhabit the Spirit World, but the Spirit World touches every part of the Middle World, the Underworld, and the Above World. Our spirit is what animates our corporeal body and gives it life. It is analogized as “breath” (by the Orlanth, Praxians, and many Hsunchen), “heat” (by the Doraddi), “beast soul” (by the Pelorians), and so on. When it is gone, we are without life.
Not only do humans, animals, and plants have spirits, but everything else does as well. Every wind has a spirit that animates it. Every drop of water has a little spirit that inhabits it. Big winds have more powerful spirits than little breezes, and the spirit of a river is more powerful than that of a drop of water. The most powerful spirits are called “gods.” For example, the vast storm that permeates all of the Middle Air has a great spirit that its slaves call “Orlanth,” but powerful shamans know as Storm King. The gods are the masters of the Runes, who made Glorantha and then nearly destroyed it in the Great Darkness.
Those with the ability to communicate with spirits can see these discorporate beings, commensurate with the strength of their spiritual organs. Most spirit magicians can communicate only with those spirits that are comparable to their own; the gods are too immense for all but the most powerful shamans to even fully perceive, let alone communicate with. Storm Bull is too great a spirit for any but the most powerful shamans to normally communicate with, but he speaks with and aids the Praxians because of his kinship with them.
Most spirits are embodied in the Middle World – as the spirits of animals, plants, and things – but some spirits are disembodied and long for bodies to inhabit. Spirits without their own bodies want them, or want to feed off of those who do have bodies. These are the spirits of the dead, disease, and other malevolent things. Some are benevolent, but most are harmful and dangerous. Only shamans know how to deal with all sorts of disembodied spirits, although some cults and sorcerers know magic that can cast out specific types of spirits (e.g., Chalana Arroy can cast out disease spirits, Humakt can fight the spirits of the dead, etc).
In game terms, spirit magic generally employs charms that houses a spirit. When a charm is made, the maker negotiates with the spirit to see what it wants. A spirit who can Light Fires might want want to be in a firestick, or a spirit who is Sharp as a Bulls Horn may be content in a wooden ring. Spirits have their own ideas of what they want and they may or may not be the same as human needs or desires. The spirit also informs the maker of the taboos that must be obeyed if the spirit is to remain helpful.