Fairies in the context of "Familiar spirit"

In European folklore of the medieval and early modern periods, familiars (strictly familiar spirits, as "familiar" also meant just "close friend" or companion, and may be seen in the scientific name for dog, Canis familiaris) were believed to be supernatural entities, interdimensional beings, or spiritual guardians that would protect or assist witches and cunning folk in their practice of magic, divination, and spiritual insight. According to records of the time, those alleging to have had contact with familiar spirits reported that they could manifest as numerous forms, usually as an animal, but sometimes as a human or humanoid figure, and were described as "clearly defined, three-dimensional... forms, vivid with colour and animated with movement and sound", as opposed to descriptions of ghosts with their "smoky, undefined form[s]".

When they served witches, they were often thought to be malevolent, but when working for cunning folk, they were often considered benevolent (although there was some ambiguity in both cases). The former were often categorized as demons, while the latter were more commonly thought of and described as fairies. The main purpose of familiars was to serve the witch, providing protection for them as they came into their new powers.