A short knee length dress shape of the 1920s, lightweight wool, satin, silk and velvet fabrics are usual and often cut to reveal the shoulders and arms. examples

a dress suitable for formal occasions

a dress that is worn to cocktail parties and other formal social events

a dress worn for late afternoon and evening social functions; dressier than afternoon dress, but not as formal as a full-length evening gown.

A cocktail dress or cocktail gown is a shorter-length lady's gown worn at cocktail parties and other semi-formal and formal occasions. Less elaborate versions may be worn at semi-formal occasions when gentlemen are in dark suits. (When gentlemen are in business suits, ladies also wear dress suits or "good" afternoon dresses).