In folklore and ethnography, a spirit is an "immaterial being", "supernatural agent", the "soul of a person", an "invisible entity", or the "soul of a seriously suffering person". Often spirits have an intermediate status between gods and humans, sharing some properties with gods (Incorporeality, greater powers) and some with humans (finite, not omniscience).

Thus, a spirit would have a form of existing and thinking; it would exist without being generally visible; often popular traditions endow it with miraculous powers and more or less occult influences on the physical world.

Spirits can be classified according to the science in charge of their study: angels and demons belong to theology, ghosts and spirits to metapsychology, fairies and gnomes to folklore, the souls of the dead to the cult of the dead, spiritualism, magic, necromancy. However, there are frequent hesitations.^{[incomprehensible]}

Alternatively, a historical approach can be taken. Medieval texts are full of planetary spirits (inhabitants of the planets), angelic spirits (angels, archangels, guardian angels, etc.), nature spirits (undines, sylphs, etc.), place spirits, etc.

Spirits are often classified by the worlds they inhabit: underworld, earth, atmospheric, or heaven.

They are also classified as good and bad, or as neutral: the word "devil" is pejorative, but the word "demon" changes the value.

In 17th century Europe, spirits included angels, demons, and disembodied souls. Dom Calmet, a specialist on the subject, explained that he was writing "on the apparitions of angels, demons and souls separated from the body". The Lalande dictionary follows suit: "God, angels, demons, disembodied souls of people after death are the spirits".

In some cultures, the "spirits of nature" refers to the elementals, spirits linked to the four classical elements: gnomes for earth, undines for water, sylphs for air, salamanders for fire).