Cleavage
The area that is viewed either between breasts, or preferably at the contact point between breasts. Often one of the determining factors when the male mind subconsciously rates a woman on the bang-ability scale. Less cleavage is preferred when titty fucking. Often women will expose their cleavage when leaning forward in order to appear desirable, although this should only be done with firm, well rounded breasts.
Some times (though rarely) referred to as the "Boob border"
"You know, I have to be honest. I may love her for who she is, but I have to admit that i fantasise about getting a titty fuck from Caitlin."

"In my opinion Joelle's cleavage should be elected president."

"Dude, I wish sexual harassment wasn't against the law. I would die happily drowning in Kait's cleavage."