The nipple is a raised region of tissue on the surface of the breast from which, in females, milk leaves the breast through the lactiferous ducts to feed an infant. The milk can flow through the nipple passively or it can be ejected by smooth muscle contractions that occur along with the ductal system. Male mammals also have nipples but without the same level of function, and often surrounded by body hair.

The nipple is surrounded by the areola, which is often a darker colour than the surrounding skin. A nipple is often called a teat when referring to non-humans. "Nipple" or "teat" can also be used to describe the flexible mouthpiece of a baby bottle. In humans, the nipples of both males and females can be stimulated as part of sexual arousal. In many cultures, human female nipples are sexualized, or regarded as sex objects and evaluated in terms of their physical characteristics and sexiness. Some cultures have little to no sexualization of the nipple, and going topless presents no barrier.