A fairy is a type of mythological being or legendary creature, a form of spirit, often described as metaphysical, supernatural or preternatural.
The word "fairy" derives from the fae of medieval Western European (Old French) folklore and romance, one famous example being Morgan le Fay. "Fae-ery" was therefore everything that appertains to the "fae", and so the land of "faes", all the "faes". Finally the word replaced its original and one could speak of "a faery or fairy", though the word "fey" is still used as an adjective.
Fairies resemble various beings of other mythologies, though even folklore that uses the term "fairy" offers many definitions. Sometimes the term describes any magical creature, including goblins or gnomes: at other times, the term only describes a specific type of more ethereal creature.
The origins of the belief in fairies are unclear and perhaps the reasoning is that many different cultures have many different stories. Some consider them a form of Angel, perhaps a demoted angel that was caught in between heaven and hell when Lucifer lead the revolt against God. Others hold that they were not good enough for heaven, but not evil enough for hell.
In Africa, the Aziza are a beneficent fairy race, specifically from Dahomey. Living in the forest, they provide good magic for hunters. They also give both practical and spiritual knowledge to people. Aziza means "near to God", which may put them on the level of angelic creatures.
An alux is the name given to a type of sprite or spirit in the mythological tradition of certain Maya peoples from the Yucatán Peninsula and Guatemala. Aluxob are conceived of as being small, only about knee-high, and in appearance resembling miniature traditionally dressed Maya people. Tradition holds that aluxob are generally invisible but are able to assume physical form for purposes of communicating with and frightening humans as well as to congregate together. They are generally associated with natural features such as forests, caves, stones, and fields but can also be enticed to move somewhere through offerings. Their description and mythological role are somewhat reminiscent of other sprite-like mythical entities in a number of other cultural traditions (such as the Celtic leprechaun), as the tricks they play are similar.
The word “duende” is sometimes used interchangeably with “alux”. Duende is a Spanish word for a supernatural creature (commonly a goblin) or force. In fact, because of such striking similarities, some suspect that the Maya’s belief of aluxob developed through interactions with the Spanish or pirates during the 16th century. Pirates of that era were often from the British Isles, where belief in faeries was quite common, especially amongst those of lower socio-economic class (as pirates generally would have been). However, the Maya themselves would claim that the alux are the spirits of their ancestors, or the spirits of the land itself, preceding contact with Western civilization.
Indeed, the idea that they are spirit of the dead comes from the Irish Gaelic bean si which means "fairy woman" but which is commonly translated as banshee, a type of ghost.
Elemental alchemists believed that fairies were spirits of the air, just as gnomes were spirits of the earth.
The belief that fairies were inherently evil began around the time of the growth of puritanism, although few folklores hold them to be totally good creatures. They are generally portrayed as being mischievous and love playing tricks on humans.
Because of their diminutive size, it is sometimes believed that a cat will keep them away from a household, as they would make a tasty snack for a hunting feline. In more recent literature, Kim Harrison plays this up in her post plague world, in which both pixies and fairies are wary of the witch's favorite familiar.
Many of the Irish tales of the Tuatha Dé Danann refer to these beings as fairies, though in more ancient times they were regarded as Goddesses and Gods. The Tuatha Dé were spoken of as having come from Islands in the north of the world, or, in other sources, from the sky. After being defeated in a series of battles with other Otherworldly beings, and then by the ancestors of the current Irish people, they were said to have withdrawn to the sídhe (fairy mounds), where they lived on in popular imagination as "fairies." (My bean is rather enamored of the old Celtic faery lore and the sidhe.)
Currently art and literature paints them as diminutive beings with the wings of insects for butterflies, but this was not always the case. Some held them to be of a size with humans, while others said they were so small they could ride on the backs of birds.
The tales and references are long and stem throughout the world. It is interesting how fairies have captured the imagination, and continue to be popular in literature, film and music.