A term from Paracelsus. Sylphs are elemental intelligences related to the subtle, intangible aspect of nature (air).
"Just as visible Nature is populated by an infinite number of living creatures, so, according to Paracelsus, the invisible, spiritual counterpart of visible Nature (composed of the tenuous principles of the visible elements) is inhabited by a host of peculiar beings, to whom he has given the name elementals, and which have later been termed the Nature spirits. Paracelsus divided these people of the elements into four distinct groups, which he called gnomes, undines, sylphs, and salamanders. He taught that they were really living entities, many resembling human beings in shape, and inhabiting worlds of their own, unknown to man because his undeveloped senses were incapable of functioning beyond the limitations of the grosser elements...
While the sages said that the fourth class of elementals, or sylphs, lived in the element of air, they meant by this not the natural atmosphere of the earth, but the invisible, intangible, spiritual medium--an ethereal substance similar in composition to our atmosphere, but far more subtle. In the last: discourse of Socrates, as preserved by Plato in his Phædo, the condemned philosopher says:
"And upon the earth are animals and men, some in a middle region, others (elementals] dwelling about the air as we dwell about the sea; others in islands which the air flows round, near the continent; and in a word, the air is used by them as the water and the sea are by us, and the ether is to them what the air is to us. More over, the temperament of their seasons is such that they have no disease [Paracelsus disputes this], and live much longer than we do,
and have sight and bearing and smell, and all the other senses, in far greater perfection, in the same degree that air is purer than water or the ether than air. Also they have temples and sacred places in which the gods really dwell, and they hear their voices and receive their answers, and are conscious of them and hold converse with them, and they see the sun, moon, and stars as they really are, and their other blessedness is of a piece with this." While the sylphs were believed to live among the clouds and in the surrounding air, their true home was upon the tops of mountains.
In his editorial notes to the Occult Sciences of Salverte, Anthony Todd Thomson says: "The Fayes and Fairies are evidently of Scandinavian origin, although the name of Fairy is supposed to be derived from, or rather [is] a modification of the Persian Peri, an imaginary benevolent being, whose province it was to guard men from the maledictions of evil spirits; but with more probability it may be referred to the Gothic Fagur, as the term Elves is from Alfa, the general appellation for the whole tribe. If this derivation of the name of Fairy be admitted, we may date the commencement of the popular belief in British Fairies to the period of the Danish conquest. They were supposed to be diminutive aerial beings, beautiful, lively, and beneficent in their intercourse with mortals, inhabiting a region called Fairy Land, Alf-heinner; commonly appearing on earth at intervals--when they left traces of their visits, in beautiful green-rings, where the dewy sward had been trodden in their moonlight dances."
To the sylphs the ancients gave the labor of modeling the snowflakes and gathering clouds. This latter they accomplished with the cooperation of the undines who supplied the moisture. The winds were their particular vehicle and the ancients referred to them as the spirits of the air. They are the highest of all the elementals, their native element being the highest in vibratory rate. They live hundreds of years, often attaining to a thousand years and never seeming to grow old. The leader of the sylphs is called Paralda, who is said to dwell on the highest mountain of the earth. The female sylphs were called sylphids.
It is believed that the sylphs, salamanders, and nymphs had much to do with the oracles of the ancients; that in fact they were the ones who spoke from the depths of the earth and from the air above.
The sylphs sometimes assume human form, but apparently for only short periods of time. Their size varies, but in the majority of cases they are no larger than human beings and often considerably smaller. It is said that the sylphs have accepted human beings into their communities and have permitted them to live there for a considerable period; in fact, Paracelsus wrote of such an incident, but of course it could not have occurred while the human stranger was in his physical body. By some, the Muses of the Greeks are believed to have been sylphs, for these spirits are said to gather around the mind of the dreamer, the poet, and the artist, and inspire him with their intimate knowledge of the beauties and workings of Nature. To the sylphs were given the eastern corner of creation. Their temperament is mirthful, changeable, and eccentric. The peculiar qualities common to men of genius are supposedly the result of the cooperation of sylphs, whose aid also brings with it the sylphic inconsistency. The sylphs labor with the gases of the human body and indirectly with the nervous system, where their inconstancy is again apparent. They have no fixed domicile, but wander about from place to place--elemental nomads, invisible but ever-present powers in the intelligent activity of the universe." —Manly P. Hall, Secret Teachings of All Ages
"The four elements of Nature—earth, fire, water, and air—are merely condensations of the four types of ether. These four varieties of ether are densely populated by innumerable elemental creatures of Nature. The salamanders live within the fire (the Tejas Tattva). The ondines and nereids live within the water (the Apas Tattva). The sylphs live within the clouds (the Vayu Tattva). The gnomes and pygmies live within the earth (the Prithvi Tattva)... The physical bodies of the sylphs are the elementals of the plants belonging to the signs of air." —Samael Aun Weor, Esoteric Medicine and Practical Magic