Tiny creatures that look like perfectly formed humans with insect wings.
They are extremely vain and quarrelsome, liking nothing better than to serve as decoration (see Christmas Ornaments). Fairies have their own weak form of magic, which they use primarily to avoid being eaten by predators such as the Augurey. According to Scamander, fairies are held to have very limited intelligence, and they do not use any form of language that humans understand (but see languages) (FB).
Professor Flitwick decorates his classroom for Christmas with living fairies (PA10).
The rose garden conjured for the Yule Ball featured hundreds of fairies (GF23).
Fairy eggs are the preferred food of Bowtruckles (OP13).
Fairies are common in folklore the world over, usually depicted as small ethereal beings which live out of sight of humans, often in woodlands. Fairies have magical powers to fly, cast spells, and predict the future. They can be friendly but are sometimes depicted as mischievous or even malevolent. Ms. Rowling’s version of fairies is quite different from the traditional type, more like insects than intelligent nature spirits. (The Lexicon page 109).