breasts apart
When the breasts rest far apart, either due to gravity pulling them apart or due to being physically held apart.
As a rule of thumb, the breasts should point away from each other and the skin over the sternum should be visible.
The opposite of cleavage. Not for when breasts are too small to touch, or when they don't touch because of something between breasts.
Examples
See also
This tag implicates breasts (learn more).
