时效 (shí xiào) is a compound noun meaning 'timeliness' or 'validity period.' It combines 时 (shí), meaning 'time,' and 效 (xiào), meaning 'effect' or 'efficacy.' Together, they convey the idea that something's usefulness or legal force depends on occurring within a specific time frame. This word emphasizes not just chronological passage but the functional relevance of timing — for instance, news loses timeliness if reported too late, or a contract clause expires after its validity period ends.

The term appears frequently in formal, administrative, legal, and technical contexts — such as law (statute of limitations), logistics (shelf life of goods), journalism (news deadlines), and IT (cache expiration). It is rarely used in casual daily speech and carries a somewhat technical or institutional tone. While it can refer to abstract concepts like 'the timeliness of feedback,' it more often denotes a concrete, bounded duration during which an action, document, or item remains effective or acceptable.