Sylph is a faux-mythological creature in the Western tradition. "Sylph" has passed into general language as a term for minor spirits, elementals, or faeries of the air. Fantasy authors will sometimes employ sylphs in their fiction. In current usage, the term is applied to a feminine spirit or fairy, and is often used in a figurative sense of a graceful, slender girl or young woman.
The term originates in Paracelsus, who describes sylphs as invisible beings of the air, or elementals of air. There is no substantial myth associated with them. As alchemy in the West derived from Paracelsus, alchemists and related movements, such as Rosicrucianism, continued to speak of sylphs in their hermetic literature.
The first mainstream western discussion of sylphs comes with Alexander Pope. In Rape of the Lock, Pope satirizes French Rosicrucian and alchemical writings when he invents a theory to explain the sylph. In a parody of heroic poetry and the "dark" and "mysterious" literature of pseudo-science, and in particular the sometimes esoterically Classical heroic poetry of the 18th century in England and France, Pope pretends to have a new alchemy, where the sylph is the mystically, chemically condensed humor of peevish women.
In Pope's poem, women who are full of spleen and vanity turn into sylphs when they die because their spirits are too full of dark vapors to ascend to the skies. Belinda, the heroine of Pope's poem, is attended by a small army of sylphs, who foster her vanity and guard her beauty.
This is a parody of Paracelsus, inasmuch as Pope imitates the earnest pseudo-science of alchemy to explain the seriousness with which vain women approach the dressing room. In a slight parody of the divine battle in John Milton's Paradise Lost, when the Baron of the poem attempts to cut a lock of Belinda's hair, the sylphs interpose their airy bodies between the blades of the scissors (to no effect whatever).