'Yí fù' is a kinship term meaning 'maternal aunt’s husband' — the husband of one’s mother’s sister. The first character 姨 (yí) specifically denotes a maternal aunt (distinguishing her from a paternal aunt, who is 姑姑 gūgu), while 父 (fù) means 'father' or 'male elder,' here used to indicate the marital relationship and male status. Together, they form a compound noun that reflects Chinese kinship naming conventions, where relationships are precisely encoded by combining relational terms with gender or generational markers.

This term is used in formal family introductions, written documents like family trees, or respectful spoken address (e.g., when children refer to or speak about this relative). It is not typically used as a direct form of address — instead, people often say 阿姨 (āyí) for the aunt and may refer to her husband as 姨父 only when clarifying family structure. Unlike English, which lacks a single-word equivalent, Mandarin uses precise, compound terms to distinguish maternal and paternal sides clearly.