'Yīn qīn' literally combines 姻 (yīn), meaning 'marriage' or 'matrimonial', and 亲 (qīn), meaning 'relative' or 'kin'. Together, it refers specifically to relatives acquired through marriage — not by blood, but by becoming part of a spouse’s family. This includes your spouse’s parents (your in-laws), siblings (your brothers- and sisters-in-law), their children (your nieces and nephews by marriage), and other extended family members connected solely through the marital bond.

The term is formal and neutral in register, commonly used in legal, familial, and sociological contexts. Unlike 亲戚 (qīnqi, 'relatives' broadly), 姻亲 explicitly excludes blood relatives and focuses only on affinal ties. It contrasts with 直系亲属 (zhíxì qīnshǔ, 'direct-line relatives') and 旁系亲属 (pángxì qīnshǔ, 'collateral relatives'), both of which refer to blood relations. Understanding this distinction helps learners navigate Chinese family terminology accurately.