In Mozart's world: French Queen Marie-Antoinette, 1775, and decolletage

Marie-Antoinette, 1775, Musée Antoine Lécuyer
Originally uploaded by trudeau

Décolletage (or décolleté, its adjectival form, in current French) is the upper part of a woman's torso, comprising her neck, shoulders, back and chest, that is exposed by the style of her clothing. Décolletage is a French word which is derived from decolleter, meaning to reveal the neck or, more literally, "without a collar," says Wikipedia.

Gowns which exposed a woman's neck and top of her chest were very common and non-controversial in Europe from at least the 11th century. The wearing of low-cut dresses which exposed breasts were considered more acceptable than they are today; with a woman's bared legs, ankles, or shoulders being considered to be more risqué than exposed breasts.[6]

From the Victorian period onward, however, social attitudes shifted to demand a woman's breasts to be covered in public. For ordinary wear, high collars were the norm for many years.

Victorian morality reflects Queen Victoria's reign (1837–1901) and the moral climate of the United Kingdom throughout the 19th century in general, which contrasted greatly with the morality of the previous Georgian period.

Victorian morality espouses sexual restraint, low tolerance of crime and a strict social code of conduct. Due to the prominence of the British Empire, many of these values were spread across the world.