'Xiǎo yí' (小姨) is a kinship term referring specifically to one’s mother’s younger sister. The character 小 (xiǎo) means 'small' or 'younger', and 姨 (yí) means 'maternal aunt' — together, they distinguish this aunt from the mother’s older sister (大姨, dà yí). Unlike general terms like 阿姨 (ā yí), which can be used for any older woman as a polite address, 小姨 is strictly familial and denotes a precise blood relationship. It is commonly used in daily conversation when speaking about or addressing this relative directly.

This term reflects Chinese kinship naming conventions, where age order among siblings matters — hence the need for 'small' to indicate junior status. It is neutral in register: appropriate in both casual family settings and formal contexts involving relatives. Children typically use it when speaking to or about their mother’s younger sister, and adults may continue using it throughout life, even after marriage or having children of their own.