An evening gown or gown is a long flowing women's dress usually worn to a formal affair. It ranges from tea and ballerina to full-length. Evening gowns are usually made of luxurious fabrics such as chiffon, velvet, satin, organza, etc. Silk is a popular fibre for many evening gowns. Although the terms are used interchangeably, ball gowns and evening gowns differ in that a ball gown will always have a full skirt and a fitted bodice; in contrast, an evening gown can be any silhouette—sheath, mermaid, A-line or trumpet shaped—and may have an empire or dropped waist.