Décolletage (or décolleté, its adjectival form, in current French) In strict usage the term denoted the neckline, the zone extending about two handbreadths from the base of the neck down, obverse and recto. Only after the French Revolution did the décolletage become larger in the front and smaller in the back.
The International Federation of Associations of Anatomists (IFAA) has adopted the terms intermammary sulcus or intermammary cleft when referring to the area of cleavage between the breasts not including the breasts. For legal purpose it was noted by the United States federal courts that “anal cleft or cleavage” and “cleavage of the female breast” are so imprecise as to provide no guidance in defining them.
I Googled “décolletage” to make sure I was spelling it correctly in my Country Strong review, and ended up on the Wikipedia page for Cleavage_(breasts).