This once again is a subject that probably deserves multiple entries and I will likely provide those some time in the near future. However I just wanted to give a brief overview of the various types of Spirit or Spiritual Entity that mediums usually work with. This is not necessarily and exhaustive list and I may expand this later, however, it should give one a general overview.
Ancestors
When most people say they are a medium, these are the sort of being that they likely interact with. An Ancestor is to put it simply, the soul of a departed person, usually a blood relative but not always. They may be people who were so close they were as if they were family or a soul so similar to your own or may otherwise feel some kind of intense kinship with you that they are as if they are family. Working and revering Ancestors is a major part of many traditional religions from those found in many cultures of east Asia such as the spirituality of the Han Chinese people, Shinto, Thai folk religion, and numerous others as well as many forms of European Paganism and African Traditional and Diasporic religions. Ancestors are usually beneficent or at least harmless toward the living and are perhaps some of the most keenly interested in our lives. However, not all Ancestors were virtuous in life and one should take precautions so as to keep the space where you are engaging with the souls of the departed or any Spiritual Being, purified and protected. However, this is almost never a problem for most people who understand what they’re doing.
Elementals And Other Nature Spirits
Nature Spirits are what they are. These are Spirits more directly tied to the natural forces of the world and places. Spirits of forests, trees, the wind, flowers, rivers, lakes, mountains, and other various natural phenomena. Elementals are a type of nature Spirit that deal with the primary elemental powers that suffuse the universe such as Air, Fire, Water, Earth, and Spirit as described in many western mystical traditions. These Spirits though more directly tied to nature do possess links to other aspects of existence such as emotions, thoughts, and certain arts. They may be tied more directly to the land and various occurrences found therein, but they are not utterly divorced from the sphere of human civilizations as we often think of them. They take on many forms. Some are more humanoid, some are more bestial, others may manifest as the force they are most directly linked to such as a fire Spirit manifesting as a roaring flame. There are numerous subdivisions of Nature Spirit and Elementals specifically, but I shall likely go into greater depths about these later.
Beast Spirits
When people use (or misuse) terms such as “Spirit Animal” or “Totem” these are likely what they are referring to. These can be tutelary Spirits that guide individuals which are linked to certain animals, certain Spirits similar to elemental in that they are tied to certain animal groups, or possibly the souls of deceased animals. Some may act more “feral” where others may act in a fashion similar to a human trapped in a beast’s body.
Fairies/Sidhe
Despite their reputation, the Fae folk/the Sidhe in many of the older legends are actually fair folk. In my research into how these particular Spirits have been portrayed in traditional lore, it would seem the term Sidhe could be more accurately described as a term meaning a Spirit of any sort ranging from Nature Spirits to Ancestors, but many people who deal with them would say that they constitute a special class of Spirit all their own. These Spirits while generally benign do have a penchant for mischief and are quite chaotic compared to certain others. They are wild, but they can demonstrate great subtlety and restraint when they so wish. While generally goodnatured, it should be noted that one should not trespass against them, for when roused to anger, their wrath is legendary.
Angels
Angels are the Spirit Host seemingly tied to the Abrahamic religions and their Deity, Yahweh/Allah/God among other names. They are benevolent and in themselves are comprised of many classes, very few of which actually resemble the human with wings often shown in art and pop culture. In fact, if one looks into traditional lore, they take on forms which include such seemingly alien visages as that of wheels covered with eyes. If the Sidhe/Fae are among the more wild Spirit hosts, then Angels are among the most stoic and orderly.
Domestic Spirits
Hearth and home Spirits are known in the folklore, traditional spirituality, and popular imaginations of many cultures the world over. A prime example of these would be the Domovoi of Russian/Slavic lore. These are the Spirits who guard and preside over ones dwelling and in themselves comprise many different forms.
Loa
The Loa are the myriad Divinities of Voodoo/Vodun in it’s many forms. Many westerners may find them outwardly scary, but they are not evil. They are however, based on my correspondences with people who have studied or practice one such spiritual path, very demanding. Usually they favor people aligned with ATDRs, but will reach out to others. If one is going to attempt to work with them in any capacity, one would do well to research how they are traditionally honored or better yet, enlist a practitioner of Voodoo/Vodun to help if one believes one of these Spirits is reaching out to them so as to help avoid cultural appropriation and show proper respect to the Loa. The term Loa is some times translated as Deity, but to many practitioners of Vodun they are more like powerful, if not Godlike Divinities, but not Gods themselves who happen to serve the actual distant, but beneficent Deity of these spiritual paths. I’ve seen some debate around this, but this description seems to be the most common, so I thought it should go with that just to play it safe.
Orishas
Much of what was said about the Loa can be applied to Orishas. However, where as the Loa are tied to traditions derived heavily from Fon religion, the Orisha’s are most directly tied to paths derived from traditional Yoruba religion and it’s descendants such as Candomble, Santeria, and Lukumi. I must stress that these are also very demanding Divinities, but they are not evil even people find aspects of how they are worshiped or how they manifest disquieting to people who are not quite familiar with them or those things related to them. I must also stress that one would do best to consult a Babalawo, Santero/Santera, or one other such religious specialist who follows the paths most directly tied to them if one feels an Orisha is specifically reaching out to them.
The Odd Ones
The odd ones are not really a single class of Spirit themselves, but instead comprise those Spirits who do not necessarily seem to specifically fit into any of these other groups. Many of them are outwardly off putting, but are still benign.
Deities
Now normally, one does not directly channel the power of something this powerful. Instead one feels and channels something of their power when so ever they are particularly close to them or they are reaching out to the medium. They seldom communicate with people in a very overt or direct manner, but that does not mean they are uncaring or cruel. They are not a class of Spirit but something greater. Because of their nature they are perhaps truly the most difficult to describe in their rawest essence. The closest a human can come to putting it to words may not do them justice.