标准 (biāo zhǔn) — (noun) standard, norm, criterion; (adjective) standard, correct, conforming to an established standard

标准 (biāozhǔn) covers the everyday idea of a 'standard' — both the rule itself (noun) and 'standard / proper' (adjective, e.g. 发音很标准). It's the common, neutral word; siblings like 规范 are more formal and 准则 is for principles/codes of conduct.