Sylphs (sometimes known as sylphids) are the elemental spirits of air. They are one of the four elementals, which are creatures that represent the Cardinal elements—earth, water, air, and fire. Gnomes represent the earth, undines represent the water, sylphs the air, and salamanders fire. Paracelsus, a medieval physician, alchemist, astronomer, and occultist, came up with the idea of the four elementals. Their name comes from the Greek word silphe, which means butterfly.
Sylphs live in the sky and clouds, flying freely wherever they wish. It is said that they can only travel through the air, as they become trapped in the earth, drown in the water, and burn in fire. It's also said that sylphs are mortal beings, and they can die from hunger, illness and/or physical injury. Their mortal depiction comes from them being portrayed as between spirit and creature. They've also been described as being stronger and more intelligent than humans, having an innate understanding of the universe and connections between all its parts, along with supernatural foresight. They're commonly shown as guardians, protecting secret knowledge or the environment.
Although sylphs are said to be too pure to be seen by the eyes of humans, there are multiple different depictions of them. One depiction is of tall, lithe, humanlike creatures with giant wings, large hawk eyes, and sharp/angular facial features. Another depiction is of thin, ethereal beings that change into countless different shapes as they fly through the sky. Sylphs are also sometimes illustrated as having coarse, humanoid shapes that are larger and stronger than those of regular humans. During the romantic era, their appearance was changed to resemble a dainty, fairy-like creature with graceful wings.
Sylphs have power over the skies and air. They've been delineated to have control over the wind and the clouds, and even have the ability to purify the air and control the weather itself. It's been said that the air element induces feelings of festivity, giving someone the abrupt feeling of needing to break out into song or dance.