A little black dress is an evening or cocktail, cut simply and often quite short. Fashion historians ascribe the origins of the little black dress to the 1920s designs of Coco Chanel, intended to be long-lasting, versatile, affordable, accessible to the widest market possible and in a neutral color. Its ubiquity is such that it is often simply referred to as the "LBD."
The "little black dress" is considered essential to a complete wardrobe by many women and fashion observers, who believe it a "rule of fashion" that every woman should own a simple, elegant black dress that can be dressed up or down depending on the occasion: for example, worn with a jacket and pumps for daytime business wear or with more ornate jewelry and accessories for evening. Because it is meant to be a staple of the wardrobe for a number of years, the style of the little black dress ideally should be as simple as possible: a short black dress that is too clearly part of a trend would not qualify because it would soon appear dated.
In 1926 Gabrielle "Coco" Chanel published a picture of a short, simple black dress in American Vogue. It was calf-length, straight, and decorated only by a few diagonal lines. Vogue called it “Chanel’s Ford.” Like the Model T, the little black dress was simple and accessible for women of all social classes. Vogue also said that the LBD would become “a sort of uniform for all women of taste.” Read more at http://en.wikipedia.org/wiki/Little_black_dress