A short pipe coupling that is threaded on both ends and installed between fittings.
The nipple is a raised region of tissue on the surface of the breast from which milk leaves the breast through the lactiferous ducts. The milk can flow through the nipple passively or it can be ejected by smooth muscle contractions that occur along the ductal system. The nipple is surrounded by the areola which is often a darker color than the surrounding skin. It is often called a teat when referring to non-humans. Teat can also be used to describe the flexible mouthpiece of a baby bottle. In humans, 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."