A pillbox hat is a small hat, usually worn by women, with a flat crown, straight, upright sides, and no brim.
The modern woman's pillbox hat was invented by milliners in the 1930s, and gained popularity due to its elegant simplicity. Pillbox hats were made out of wool, velvet, organdy, mink, lynx or fox fur, and leopard skin, among many other materials. They were generally designed in solid colors and were unaccessorized, but could include a veil.
Jacqueline Kennedy, First Lady of the United States from 1961 to 1963, was well known for her "signature pillbox hats", designed for her by Halston. Jackie Kennedy was actually wearing a pink one to match her outfit on the day of her husband President John F. Kennedy's assassination in Dallas, Texas (November 22, 1963).