Wiktionary
n. (context chiefly UK idiomatic sometimes capitalized English) On one hand, the members of the city, borough, or similar community near a university and, on the other hand, the students and faculty of the university itself, especially when understood as rivals in a state of tension or conflict.
Wikipedia
Town and gown are two distinct communities of a university town; "town" being the non-academic population and "gown" metonymically being the university community, especially in ancient seats of learning such as Oxford, Cambridge, Durham, Edinburgh and St Andrews, although the term is also used to describe modern university towns as well as towns with a significant public school. The metaphor is historical in its connotation but continues to be used in the literature on urban higher education and in common parlance.
Usage examples of "town and gown".
Quiet, polished Neto turned out to be quite a ladies man, and he cut a major streak through the girls of both town and gown.
There is powerful rivalry in Salterton society between town and gown, military and civil service, as everybody knows.