Wikipedia
Velificatio is a stylistic device used in ancient Roman art to frame a deity by means of a billowing garment. It represents "vigorous movement," an epiphany, or "the vault of heaven," often appearing with celestial, weather, or sea deities. It is characteristic of the iconography of the Aurae, the Breezes personified, and one of the elements which distinguish representations of Luna, the Roman goddess of the Moon, alluding to her astral course.
A figure so framed is a velificans (plural velificantes). Not all deities are portrayed as velificantes, but the device might be used to mark a member of the Imperial family who had been divinized (a divus or diva).
Velificatio is a frequent device in Roman art, including painting, mosaic, relief, and sculpture, though it poses technical difficulties for freestanding sculpture. The Athenian sculptor Praxiteles was able to achieve it. The term is also used to describe Hellenistic art. The device continued to be used in later Western art, in which it is sometimes described as an aura, "a breeze that blows from either without or from within that lifts the veil to reveal the face of an otherwise invisible being."