百年好合 is a traditional Chinese wedding blessing expressing the wish for a couple to enjoy a lifetime of harmony, love, and mutual understanding. Literally, it means 'a hundred years of harmonious union' — 百年 (bǎi nián) symbolizes a long, full life; 好 (hǎo) means 'good' or 'harmonious'; and 合 (hé) means 'to unite', 'to join together', or 'in harmony'. Though 'hundred years' is hyperbolic, it reflects deep cultural value placed on marital longevity and emotional unity.

This phrase is almost exclusively used in wedding contexts: written on red wedding scrolls, spoken during ceremonies, printed on gifts, or included in congratulatory messages. It carries formal, poetic, and auspicious connotations — never used casually or for non-marital relationships. While it sounds like a description of an ongoing state, it functions as a fixed blessing rather than a descriptive noun in everyday speech.