时效性 is a noun that refers to the property of being time-sensitive or having a limited window of relevance. It combines 时效 (time effectiveness / statute of limitations) with 性 (-ness suffix). You'll encounter it in contexts where information, products, or legal claims lose their value or validity after a certain time — news articles, food expiration dates, legal deadlines, and data analysis all have 时效性. The word is more abstract than just 'timeliness' — it implies a built-in expiry or a shelf life.