milk - a) a white or yellowish emulsion secreted by the mammary glands of female mammals for suckling their young and usu. consisting of fats, proteins, sugars, vitamins, and minerals suspended in water; b) cow's milk or, sometimes, that of goats, camels, etc., drunk by humans as a food or used to make butter, cheese, casein products, etc.; c) any liquid like this, as the juice of various plants or fruits (e.g., coconut milk) or any of various emulsions.