‘案发’ is a compound noun meaning ‘the occurrence of a crime or incident,’ literally combining 案 (àn, ‘case’ or ‘legal matter’) and 发 (fā, ‘to happen’ or ‘to occur’). It functions as a time-related noun phrase indicating the moment or location when an illegal or notable event took place. It’s commonly used in formal, official, or journalistic contexts—especially in police reports, news headlines, and legal documents—to refer to the point at which a crime began or was discovered.

The term carries a neutral-to-serious register and implies investigation is likely underway. Unlike general verbs like ‘发生’ (fāshēng), ‘案发’ specifically signals that the event qualifies as a criminal case or official incident—not just any accident or mishap. It often appears with temporal or locative modifiers (e.g., ‘案发当天’, ‘案发地点’) and rarely stands alone without context. Learners should note it’s not used for non-criminal events—even serious accidents—unless authorities treat them as criminal investigations.