The udder is the big soft bag of milk that hangs under the back part of a cow, and also under a goat, a sheep, or a female buffalo. It has teats on it — the small parts a calf sucks, or a farmer pulls or attaches a machine to. It is a plain farm word, not a rude one and not a scientific one; a farmer, a vet, a children's book about a farm all use it happily. English keeps it strictly for these animals: we do not say it about a human, and about a dog or a pig people usually say teats rather than udder. It is nearly always singular, because although there are several teats, the whole bag counts as one thing — you say a cow's udder, not a cow's udders. Sometimes writers use it for a laugh, to describe something heavy and swinging, but that is joking and slightly rude, so it is not a use to copy.

（牛、羊等的）乳房、乳袋；台灣農牧場上常說「牛的乳房」，口語也講「奶包」。中文的「乳房」人和動物都能用，英文的 udder 只用在動物身上。