保密 (bǎomì) literally combines 保 (bǎo, 'to protect') and 密 (mì, 'secret' or 'confidential'). Together, it means 'to keep confidential' or 'to maintain secrecy'. It functions primarily as a verb, indicating the active effort to prevent sensitive information from being disclosed. The word implies responsibility and intentionality — not just silence, but deliberate safeguarding.

This term is commonly used in professional, medical, legal, and governmental contexts where privacy and data protection matter. For example, doctors must 保密 patient records; companies require employees to sign confidentiality agreements (保密协议). While it can occasionally appear as a noun (e.g., in phrases like 加强保密), its core usage is verbal and transitive — it usually takes an object (e.g., 保密信息, 保密数据). It carries a formal, serious register and is rarely used in casual conversation about everyday secrets.