cleavage |ˈklēvij|
noun
a sharp division; a split : a system dominated by the class cleavage.
• the hollow between a woman’s breasts when supported, esp. as exposed by a low-cut garment.
• Biology cell division, esp. of a fertilized egg cell.
• the splitting of rocks or crystals in a preferred plane or direction.

(è lo spartitette) (l’ho trovato in questa ricerca, cosa pensavate)