乳沟是指人类女性乳房间的夹缝凹处，穿着低领服装（如晚装、泳装或吊带服）时可见。乳房越丰满和越坚挺者，乳沟越明显。未发育和平胸的女性没有明显的乳沟。在某些文化中，乳沟作为女性增加性感的手法。

乳沟是人类独有的特征。其他灵长类的胸部较平坦，只有在排卵时乳房才会增大，只有人类的乳房在青春期后一直维持一定大小；演化心理学家C. B. Crawford和D. Krebs认为乳沟可以使男性增加对女性的注意和投资，即使她们不处于生育期。

英国著名动物学家德斯蒙德·莫利斯在其著作《裸猿》中认为，乳沟是模仿股沟。

在2009年香港的少女模特儿热潮后，事业线演变成女性乳沟的代称，意指女明星的星路之上，因为露乳沟就会增加曝光度，对事业发展有所助益。

Cleavage is the area between a woman's breasts lying over the sternum, and normally refers to what is visible with clothing that includes a low-cut neckline. In some cultures, display of cleavage is considered aesthetic or erotic, and may be associated with garments with low necklines that expose or highlight cleavage, such as ball gowns, evening gowns, lingerie, and swimwear. In these cultures, women have throughout history sought to enhance their physical attractiveness and femininity, within the context of changing fashions and cultural-specific norms of modesty of the time and place. The methods practised in appropriate contexts have included the accentuation and partial display of breasts, including cleavage. In some cultures any display of cleavage may be culturally taboo, illegal or otherwise socially disapproved.