Faery -- derived from the people called The Tuatha De Danann. Were they human? Were they gods? What were they? We can only guess, however, there position in ancient Ireland was so magnificient that, even if they were humans, they became divine and thus were looked upon as gods. There is no proof of their existence as a people, which leads this author to believe that they were, indeed, gods. After their disappearance from Ireland, they became known as the Faery. As we now know, there is quite a lineage attached to this one word, which is quite a loaded word today and has come to mean about twenty different classes of beings.
Elementals -- energies aligned to the four raw elements. These energies have been cartoonized into four creatures: earth -- gnomes; air -- slyphs; fire -- salamanders; water -- undines. The elemental creatures were developed as a way to explain the nature of the element and how the shape one could use to visualize when conjuring the elements for manipulative purposes. Are these four classes of creatures now known as the elementals real? You betcha. After several hundreds of years worth of human investment and development... their real. We might say that, in truth, elementals are man-made. In truth, an elemental is the life-force of an element and not a cute little image, as those borrowed from the kingdom of the nature spirits.
Nature Spirits -- the beings of the otherworld that existent within a realm that we now call "betwixt and between." Deva's and the creatures most commonly mistaken as or labeled as "fairies, faeries, feys, fays" are the helpers and keepers of nature. This author also places totem animals into this realm, as totem animals are nature spirits, too. Most of the "fairies" described in the writings published by the Theosopical Society are nature spirits, i.e. garden fairies, water babies, storm dragons, etc.. The shapes of the creatures called elementals were borrowed from nature spirits. This is why there is a great confusion when it comes to elementals and nature spirits. It is quite possible, that angels and demons could be placed under this category, but on that one, as of yet, I'm not quite sure or convinced this would be correct. As for ghosts, definitely not nature spirits, but their own class.
Sidhe -- ah, now we come to a name that confuses even some who follow the Faery-Faith Traditions. What is the difference between the Faery (TDD) and the Sidhe? The Sidhe, the Shining Ones, who came from the stars. Well, mention of them is older than the TDD and yet mingled with the TDD, thus, the Sidhe is the one word we can use to encompass the entire Irish pantehon of Gods and Goddesses. The Sidhe are divine, godhead, divinity that rolls off the tip of the tongue, conjurs the most brilliant of light and far exceeds human understanding. The Sidhe are of the stars and are limitless and much larger in meaning then is possible to convey through description.A revolution within my own heart and mind is the redistribution of the term Faery. Rather than discontinuing the use of Faery, a word that is more than a mere word, a word that at one time was a huge as "Sidhe," I've now relegated the word "Faery" as a term used to describe a space in being, a realm, the otherworld. Thus, "in Faery" or "away to Faery" or "it's Faery" now represents the realm in which the Sidhe dwell. Now, I perfer to use the term "Sidhe" when refering to the Divine Gods & Goddesses of the Irish Faery-Faith Tradition.
Medieval romances become scattered with references to different types of fairy, and thus, the literary world of fairies are born.
In the Literary Faery classification we find several types, diminutive, Elizabethan, and Jacobean.