有效 (yǒu xiào) is an adjective meaning 'effective' or 'having effect.' It literally combines 有 (yǒu, 'to have') and 效 (xiào, 'effect' or 'result'), so the compound expresses the idea of 'having an effect' — that something produces the intended or desired outcome. It’s commonly used to describe treatments, methods, measures, rules, or communication that successfully achieve their purpose.

This word frequently appears in formal, professional, and everyday contexts — especially in health, education, law, and technology. For example, a medicine may be described as 有效 if it relieves symptoms; a policy is 有效 if it solves a problem. It often follows a noun (e.g., 治疗方法有效 — 'the treatment method is effective') or appears after 是 (shì) in predicate constructions (e.g., 这个建议是有效的 — 'this suggestion is effective'). Unlike some English adjectives, 有效 is rarely used attributively before a noun without additional structure (e.g., you wouldn’t normally say *有效方法 without modification like 一种有效的方法).