Spirit

Spirits are the magical beings who inhabit, are from, or are related to the hidden World of Spirits.

It is thought that the Spirit World existed first and the great spirits who lived there created the mortal world.

Classification
In The Wizard, the Witch, and the Wild One, spirits may be celestials, fiends, fey, etc. Gods and monsters may be kin and the word "god" simply refers to a great spirit instead of a deity.

It appears that Imperial wizards may categorize spirits along a spectrum of celestial to fiend, with a separate classification for nature spirits. It is unclear if this is a widely accepted classification or one unique to the Imperial worldview.

Wild Ones
Wild Ones are a subcategory of spirits, perhaps fey in origin. Wild Ones could also refer to spirits who are related to The Great Bear and/or live in the Wild Forest. Exactly what makes a spirit a Wild One is currently unclear.

Names & Titles
A spirit's name holds great power, such that anyone who knows a spirit's name has power over them. Thus, spirits often use titles instead of their names (e.g. The Great Bear). The most powerful spirits have multiple titles (e.g. The Man in Black), which help conceal the spirit's true form. Mortals can refer to spirits by their title, or more generally as honored friends or wild ones.

Named Characters
See the Spirits category for a full list of named characters who are spirits.