母乳 literally combines 母 (mǔ), meaning 'mother', and 乳 (rǔ), meaning 'milk' or 'breast'. Together, they form the precise term for milk produced by a human mother’s mammary glands — breast milk. It is a biologically rich fluid containing antibodies, nutrients, and enzymes essential for infant development and immunity.

This word is used almost exclusively in medical, parenting, and public health contexts — for example, in discussions about breastfeeding benefits, lactation support, or infant nutrition guidelines. Unlike general terms like 牛奶 (cow’s milk) or 奶 (milk, generic), 母乳 carries strong connotations of natural nourishment, maternal care, and early-life health. It is not used metaphorically or for animal milk; for that, terms like 羊乳 (goat milk) or 牛乳 (cow milk) are employed.