留宿 means 'to stay overnight' — literally, 'to remain (留) and lodge (宿)'. The character 留 conveys staying or remaining in a place, while 宿 means to sleep or lodge, especially overnight. Together, they form a compound verb indicating the act of spending the night somewhere other than one’s usual residence — for example, at a friend’s home, a hotel, or during travel. It is commonly used in both spoken and written Chinese, often in contexts involving hospitality, travel arrangements, or temporary lodging.

This word carries a neutral-to-formal register and implies consent or arrangement: someone is invited or permitted to stay, rather than simply sleeping somewhere unexpectedly. It is not used for habitual sleeping (e.g., your own bed), nor for brief naps. In official contexts, 留宿 may appear on signs (e.g., 'No overnight guests') or in regulations about guest registration at accommodations.