'Nǎi mā' literally means 'milk-mom' — 奶 (nǎi) refers to milk, especially breast milk or infant nourishment, and 妈 (mā) means 'mom' or 'mother'. Historically, it referred to a wet nurse who breastfed another woman’s baby, often in wealthy households. Today, it most commonly means a live-in nanny or childcare provider who cares for infants and young children, often with responsibilities beyond basic supervision — including feeding, bathing, bedtime routines, and early education.

The term carries connotations of deep personal care and trust, but its register is informal and sometimes slightly old-fashioned or regional. In modern urban settings, professional caregivers are more often called 保姆 (bǎo mǔ) or 育儿嫂 (yù ér sǎo), while 奶妈 may evoke traditional or familial contexts — such as a grandmother or long-serving family helper. It’s rarely used in formal job titles or official documents.