Fairies resemble various beings of other mythologies, though even folklore that uses the term fairy offers many definations. Sometimes the term describes any magical creature, including goblins and gnomes: at other times, the term only describes a specific type of more ethereal creature.
The word fairy derives from Middle English faierie (also fayerye, feirie, fairie), a direct borrowing from Old French faerie (Modern French feerie) meaning the land, realm or chracteristic activity (i.e. enchantment) of the legendary people of folklore and romance called (in Old French) faie or fee (Modern French fee). This derived ultimately from Late Latin fata (one of the personified Fates, hence a guardian or tutelary spirit, hence a spirit in general); cf. Italian fata, Spanish hada of the same origin.
Fata, although it became a feminine noun in the Romance languages, was originally the neuter plural ("the Fates") of fatum, past participle of the verb fari to speak, hence "thing spoken, decision, decree" or "prophetic declaration, prediction", hence "destiny, fate". It was used as the equivalent of the Greek Μοῖραι Moirai, the personified Fates who determined the course and ending of human life.
To the word faie was added the suffix -erie (Mordern English -(e)ry), used to express either a place where something is found (fishery, heronry, nunnery) or a trade or typical activity engaged in by a person (cookery, midwifery, thievery). In later usage it generally applied to any kind of quality or activity associated with a particular sort of person, as in English knavery, roguery, witchery, wizardry.
Fairies are generally described as human in appearance and having magical powers. Their origins are less clear in the folklore, being variously dead, or some form of demon, or a species completely independent of humans or angels. Folklorists have suggested that their actual origin lies in a conquered race living in hiding, or in religious beliefs that lost currency with the advent of Christianity. These explanations are not necessarily incompatible, and they may be traceable to multiple sources.
Much of the folklore about fairies revolves around protection from their malice, by such means as cold iron (iron is like poison to fairies, and they will not go near it) or charms of rowan and herbs, or avoiding offense by shunning locations known to be theirs. In particular, folklore describes how to prevent the fairies from stealing babies and substituting changelings, and abducting older people as well. Many folktales are told of fairies, and they appear as characters in stories from medieval tales of chivalry, to Victorian fairy tales, and up to the present day in modern literature.
Although in modern culture they are often depicted as young, sometimes winged, humanoids of small stature, they originally were depicted much differently: tall, radiant, angelic beings or short, wizened trolls being some of the commonly mentioned. Diminutive fairies of one kind or another have been recorded for centuries, but occur alongside the human-sized beings; these have been depicted as ranging in size from very tiny up to the size of a human child. Even with these small fairies, however, their small size may be magically assumed rather than constant.
Wings, while common in Victorian and later artwork of fairies, are very rare in the folklore; even very small fairies flew with magic, sometimes flying on ragwort stems or the backs of birds. Nowadays, fairies are often depicted with ordinary insect wings or butterfly wings.
Various animals have also been described as fairies. Sometimes this is the result of shape shifting on part of the fairy, as in the case of the selkie (seal people); others, like the kelpie and various black dogs, appear to stay more constant in form.
In some folklore Fey have green eyes and often bite. Though they can confuse one with their words, fairies cannot lie. They hate being told 'thank you', as they see it as a sign as one forgetting the good deed done, and want something that'll guarantee remembrance.