A Faery is an imagined supernatural being, now it means a small creature with magical powers (or any magical creature for that matter). Peoples from a European tradition frequently have a tradition of belief in fairies.
Versions of the mythology
One version of faeries religiously speaking is that faeries were angels who didn't take a side when Satan rebelled against god. They are doomed to live on earth forever. It can also be people whose souls were put to earth because they weren’t good enough for Heaven but not bad enough for hell. It can also be the souls of unbaptized babies.
It is claimed that superstitious British people sometimes think it’s unlucky to call them fairies and call them “Good neighbours” in an effort to placate them and make them into good neighbours. The fairies are believed to say, “Call us fairies and fairies we will be. Call us good neighbours and good neighbours we will be.”  In this tradition fairies are seen as mischievous. In Ireland superstitious people sometimes thought it was unlucky to wear green as people imagined fairies wore clothes of that colour. Belief in fairies can take a part in New Age-ism.
Pagan gods and goddesses
Some people couldn't quite stop believing in the pagan gods and goddesses of their ancestors even after they converted to Christianity. So the Goddesses became faeries or fairies. The pagan gods, they became *Elves, goblons etc