'旧书' literally means 'old book', but in modern Chinese it almost always refers specifically to a secondhand or used book — one that has been owned and read by someone else before. The character 旧 (jiù) means 'old' or 'former', indicating something no longer new or in its original condition; 书 (shū) means 'book'. Together, they form a compound noun that emphasizes the book’s prior use rather than its age alone — a newly printed copy of an ancient text is not an 旧书, but a recently bought novel from a thrift store is.

This term is commonly used in everyday contexts like campus book fairs, online marketplaces (e.g., Xianyu), or neighborhood secondhand shops. It carries neutral or even positive connotations — suggesting affordability, sustainability, or nostalgic charm. Unlike terms like 古籍 (gǔjí, 'ancient texts'), which refer to rare historical manuscripts, 旧书 is accessible, practical, and widely understood across all age groups.