Muggles' Guide to Harry Potter/Magic/Fairy

Overview
Fairies are tiny humanoid creatures with functional wings. They glow with their own light, which makes them useful as decorations.

Extended Description
At the Yule Ball, Harry notes that an area of lawn just outside the Entrance Hall has been turned into a sort of grotto filled with fairy lights. He thinks that this means that there are hundreds of actual fairies sitting in the conjured rose bushes and fluttering over the statuary.

Analysis
Apart from their ability to fly and their light, we have little description of fairies. Much of what we know of them comes from Magical Beasts and Where to Find Them by "Newt Scamander".