规则(guī zé) - rule, regulation; regular, orderly in Mandarin

规则 (guīzé) is a rule in the written, published sense: the rules of a game, of a competition, of a workplace. The verb that goes with it is 遵守 (zūnshǒu, to observe) and its opposite is 打破 (dǎpò) or 违反 (wéifǎn, to break).

It doubles as an adjective meaning regular or evenly patterned, most often in the negative: 不规则 (bù guīzé, irregular), used of shapes, verbs and sleeping habits alike.

Keep it apart from 法律 (fǎlǜ), which is law with the state behind it, and from 规定 (guīdìng), a specific stipulation someone has laid down. 规则 is the set; 规定 is one clause of it.