"Sylph (also called sylphid) is a mythological creature in the Western tradition. The term originates in Paracelsus, who describes sylphs as invisible beings of the air, his elementals of air. There is no known substantial mythos associated with them...
Because of their association with the ballet La Sylphide, where sylphs are identified with fairies and the medieval legends of fairyland, as well as a confusion with other "airy spirits" (e.g., in William Shakespeare's A Midsummer Night's Dream), a slender girl may be referred to as a sylph.
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. Sylphs could create giant artistic clouds in the skies with their airy wings"
(Wikipedia)