Fairies are a very real people whom one must be aligned with the frequency of to be seen. Fae, fairy, faery and faerie are actually generic names for peoples who live on the other side of space-time, known popularly as the Otherworld and scientifically as Tau Space. This realm is also known as Fairyland, Avalon and Tir na n'Og (i.e. The Land of Eternal Youth) This realm will eventually merge with our own, Sigma Space. The small ones in flowers are known as sprites and were popularized in the Victorian era. Fairies are found all across the world and are known by different names. In the West they are very associated with the Celts of the British Isles as well as Brittany, the peninsula jutting out from northwestern France. In Mediterranean countries the nymphs and satyrs have made their presence know. In Hindu mythology they are known as yakshas. They have a very rich history in Japan and are known as youkai. They have notable presences in Ontario, upstate New York and far out West in Hawai'i (particularly the menehune on the island of Kau'ai). Even in African countries there are reports of people who live "underground" in glistening castles. Merfolk are a notable presence in waters and incarnate merfolk in particular are making their presence known.
There can be a fair bit of ambiguity on whether an entity is considered a fae versus something else such as a ghost, phantom, thoughtform, angel, demonic being, elemental, nature spirit or extraterrestrial. Fae can be particularly associated with elementals and nature spirits to the point where it is difficult to differentiate with the amount of knowledge we have on them, so entities considered either variety may be included in the lore. More research is needed to know if elementals become more sentient and then commonly incarnate as fae. Fae are also associated with the veil of death; human spirits who have just passed on may head to the Otherworld and become acquainted with and/or transform into fae which creates more ambiguity. It should also be noted that a soul can be both human and fae, along with countless other races, in their shared pool of incarnations.