床单 (chuáng dān) literally combines 床 (chuáng), meaning 'bed', and 单 (dān), meaning 'sheet' or 'single layer'. It refers specifically to the large, flat piece of fabric that covers a mattress — what English speakers call a 'bed sheet'. Unlike Western usage where 'sheet' may refer to any thin fabric layer, in Chinese 床单 always denotes the top sheet placed directly over the mattress (not pillowcases or fitted sheets, which have different names). It’s a common household item used daily for hygiene and comfort.

Bed sheets in China are typically made of cotton, polyester, or blends, and come in standard sizes matching common mattress dimensions. People change their 床单 regularly — often weekly — as part of routine cleaning. The word appears frequently in contexts related to laundry, home goods shopping, hotel stays, and domestic chores. While not technically a compound with grammatical particles, its meaning is fully transparent: it's the 'sheet for the bed'.