‘暗号’ (àn hào) literally combines ‘暗’ (àn), meaning ‘dark’, ‘hidden’, or ‘secret’, and ‘号’ (hào), meaning ‘signal’, ‘call’, or ‘mark’. Together, they form a noun meaning ‘secret signal’—a prearranged word, gesture, sound, or object used to convey confidential information or confirm identity without others understanding. It implies intentionality and mutual agreement between participants, often for safety, coordination, or fun.

This term is commonly used in contexts like espionage, team activities (e.g., scouts or campers), online communities, or even playful daily interactions among friends or family. While it can evoke dramatic imagery (e.g., spy novels), in modern Chinese it’s frequently used in lighthearted, everyday situations—such as agreeing on a phrase to signal when someone wants to leave a boring party. It carries no inherent negative connotation but does suggest discretion and shared understanding.