孬 is a colloquial adjective meaning 'bad' or 'cowardly', formed by combining 不 (not) and 好 (good) — literally 'not good'. It's used in informal speech, especially in some northern dialects, to describe poor quality or a lack of courage. You'll hear it in phrases like 孬种 (coward) or 孬货 (inferior goods). It's not common in formal writing.