‘守口如瓶’ is an idiom meaning to keep a secret tightly—so tightly that your mouth is like a sealed bottle, with nothing leaking out. Literally, 守 (shǒu) means 'to guard' or 'to keep', 口 (kǒu) means 'mouth', 如 (rú) means 'as if' or 'like', and 瓶 (píng) means 'bottle'. The image evokes a bottle with a tightly closed lid: no air—or information—can escape. This idiom emphasizes discretion, self-restraint, and trustworthiness.

It’s commonly used in formal or literary contexts to praise someone’s reliability, especially when handling sensitive information—such as confidential work matters, personal confessions, or private family affairs. While it can describe habitual discretion, it’s most often applied to a specific instance of silence under pressure. It carries positive connotations of integrity and maturity, not secrecy for deceitful reasons.