副本 (fùběn) literally means 'secondary original' — 副 (fù) conveys 'secondary', 'auxiliary', or 'deputy', while 本 (běn) means 'original', 'root', or 'source'. Together, they refer specifically to an official or certified duplicate of a document — not just any copy, but one that holds legal or administrative validity, such as a photocopy of a passport, diploma, or contract stamped and verified by the issuing authority.

This term is commonly used in formal, bureaucratic, and institutional settings: government offices, schools, banks, and notary services. Unlike generic words like 复印件 (fùyìnjiàn, 'photocopy') or 拷贝 (kǎobèi, 'copy' — often digital), 副本 implies authenticity, equivalence, and official recognition. It’s also used in computing to mean 'backup copy' (e.g., data backup), reflecting its core idea of a trusted, functionally equivalent duplicate.