不对 (bù duì) literally combines 不 (bù), meaning 'not', and 对 (duì), meaning 'correct' or 'right'. Together, it functions as an adjective meaning 'incorrect', 'wrong', or 'not right'. It is commonly used in everyday spoken and written Chinese to express disagreement, factual inaccuracy, or mismatch — for example, when correcting a mistaken statement, pointing out an error in calculation, or rejecting an assumption. Unlike formal synonyms like 错误 (cuòwù), 不对 is neutral and conversational, often appearing in casual dialogue, classroom feedback, or troubleshooting contexts.

The phrase can stand alone as a short response ('That’s not right') or modify nouns with 的 (e.g., 这个答案不对 — 'This answer is wrong'). It may also appear in rhetorical questions like '这不对吗？' ('Isn’t this wrong?') to challenge logic or expectation. While it carries no strong emotional tone by itself, context and intonation can make it sound firm, puzzled, or gently corrective.