Cleavage

From Wipipedia

A Fetish outfit emphasising the wearer's cleavage

Cleavage literally means the gap between a woman's breasts. It is generally used to mean the sight of this gap, or of the breasts themselves, as revealed by a low-cut garment.

Perhaps not surprisingly, most fetish fashion designers design many of their women's garments to emphasise the wearer's cleavage.

The term is also used to describe a glimpse of the top of the buttocks (of a man or woman) over low-cut trousers.