大婶 is a polite, affectionate term used to address a woman roughly one's mother's age or older — similar to 'auntie' or 'ma'am' in English. It is commonly used for neighbors, shopkeepers, or older women you don't know personally. Unlike 阿姨 (which can also be used for younger women), 大婶 implies a certain age and respect but carries a friendly, informal warmth; be careful not to use it for anyone significantly younger than your mother, as it may imply they look older.