博士 (bó shì) is a noun meaning 'PhD' or 'doctorate' — the highest academic degree awarded by universities. Literally, 博 (bó) means 'extensive' or 'broad', and 士 (shì) originally referred to a scholar or gentleman in ancient China; together, they convey the idea of a highly learned person with broad knowledge and scholarly mastery.

The term is used both to refer to the degree itself (e.g., 'earning a PhD') and as an honorific title for someone who holds it — similar to 'Dr.' in English. In formal contexts, it’s common to address someone with a doctorate as 博士 (e.g., 张博士), though this is less frequent in casual daily speech than English 'Dr.' It appears frequently in academic, professional, and official settings, such as university faculty listings, research publications, or job titles.