Definition of side skirt in US English:

side skirt

noun

  • 1(A piece of cloth forming) either side of the lower part of a coat, dress, etc.; usually in plural (now rare).

  • 2A panel fitted to the side of a motor car or other vehicle, extending below the main bodywork between the front and rear wheels and typically also covering the wheel arches.

Origin

Early 17th century; earliest use found in George Wilkins (d. 1618), playwright and pamphleteer.