期限 (qī xiàn) is a compound noun meaning 'deadline' or 'time limit' — the fixed point in time by which something must be completed or remain valid. The first character 期 (qī) means 'period', 'term', or 'scheduled time', while the second character 限 (xiàn) means 'limit' or 'restriction'. Together, they literally convey 'a time-based limit', emphasizing a boundary in time rather than space or quantity.

This word is commonly used in formal, administrative, academic, and contractual contexts — such as project timelines, visa validity periods, loan repayment schedules, or assignment due dates. It carries a neutral-to-formal register and is rarely used in casual speech; native speakers often prefer simpler alternatives like 截止日期 (jiézhǐ rìqī) in everyday situations. 期限 is typically preceded by modifiers indicating duration (e.g., 三个月的期限 — 'a three-month deadline') or followed by verbs like 到期 (dào qī, 'to expire').