A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma, "breast". The mammary glands are arranged in organs such as the breasts in primates, the udder in ruminants, and the dugs of other animals. Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years. It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur. With humans, male lactation can occur only under specific circumstances.

स्तनग्रंथि स्तनधारी वर्ग के शरीर की एक विशेष और अनूठी ग्रन्थि है। यह ग्रंथिया स्वेद ग्रंथियो का रुपांतरण होती है । यह दूध" का स्रवण करती है जो नवजात शिशु के लिए पोषक आहार है।