严格(yán gé) - strict in Mandarin

严格 (yángé) means "strict", describing rules, standards or the person enforcing them. It shares the 严 (yán), "strict, severe", of 严肃 (yánsù), "serious", but 格 (gé) adds the sense of a fixed "standard, rule, framework", so 严格 (yángé) is specifically about how tightly a standard is applied, not about someone's facial expression.

严格 (yángé) is the natural word for strict parents (严格的父母 yángé de fùmǔ), a strict teacher (严格的老师 yángé de lǎoshī), or strict rules (严格的规定 yángé de guīdìng), and it works as an adverb too: 严格要求自己 (yángé yāoqiú zìjǐ), "to hold yourself to strict standards".

Do not confuse it with 严肃 (yánsù): a teacher can be 严肃 (yánsù), serious faced, without being 严格 (yángé), strict on rules, and vice versa; the two overlap in the English "strict/serious" but stay distinct in Chinese.