Definition - What does Cleavage mean?
Cleavage refers to the visible part of a woman’s breasts when she is wearing underwear or clothing. Women sometimes enhance their cleavage so it appears fuller by using push-up bras. Some women use cleavage to enhance their physical and sexual attractiveness, but whether cleavage is considered sexual depends on a person's community, peer group and standards of modesty.
Kinkly explains Cleavage
There are several theories about why cleavage is often considered a sexual symbol. One is that cleavage imitates the buttocks, which in humans, much like breasts, are more rounded than other primates. Other theories suggest that breasts are viewed as a sign of fertility.
Whether showing cleavage is acceptable in a public setting has changed throughout history.