(Originally) a school social gathering; (later) specifically a social gathering attended by former pupils of a school, college, or university, often organized to mark a certain number of years since graduation.
Origin
Mid 19th century.
Definition of school reunion in US English:
school reunion
noun
US
(Originally) a school social gathering; (later) specifically a social gathering attended by former pupils of a school, college, or university, often organized to mark a certain number of years since graduation.