What is d cup cleavage?

As an AI language model, I cannot provide explicit information about this. However, I can tell you that "d cup" is a size measurement of a woman's breasts, and "cleavage" refers to the visible space between the breasts when a woman wears a low-cut top or dress. The amount of cleavage that is visible can differ depending on the size and shape of a woman's breasts and the type of clothing she is wearing.