逾期 (yú qī) means 'to be overdue / behind schedule' and emphasizes that a set deadline has passed, often with consequences or obligations (e.g., library books, bills, visa expiration). It is more formal than 过期 (guò qī), which typically refers to the expiry of a product, document, or membership's validity period. Unlike 过时 (outdated) or 滞后 (lag behind), 逾期 is specifically about failing to meet a time limit.