The term flapper in the 1920s referred to a "new breed" of young women who wore short skirts, bobbed their hair, listened to the new jazz music and danced the Charleston. The name is said to come from the fact that they wore opened galoshes (boots) that flapped when they walked and danced. The cartoonist John Held is said to have depicted flappers in their galoshes but actually all the cartoons of his that I have found show the flappers in high heels with bows on the ankles.
