What is Campus?

Legal Definition
A campus is traditionally the land on which a college or university and related institutional buildings are situated. Usually a college campus includes libraries, lecture halls, residence halls, student centers or dining halls, and park-like settings.

A modern campus is a collection of buildings and grounds that belong to a given institution, either academic or non-academic. Examples include the Googleplex and the Apple Campus.
-- Wikipedia
Legal Definition
In old European law. An assembly of the people; so called from being anciently held in the open air, in some plain capable of containing a large number of persons. In feudal and old English law. A field, or plain. The field, ground, or lists marked out for the combatants in the duellum, or trial by battle.
See also
-- Black's Law Dictionary
Legal Definition
A field.
-- Ballentine's Law Dictionary