The most familiar sense of the definition of campus is certainly that of college grounds. The original definition of the word campus, according to the Online Etymology Dictionary, is "a field," probably prop. "an expanse surrounded" (by woods, higher ground, etc.) from Latin. First used in college sense at Princeton."
Driving by our local hospital the other day started me to thinking about all the additional senses of the definition that are now used.
The Merriam-Webster Online Dictionary entry for campus is:
"1 : the grounds and buildings of a university, college, or school 2 : a university, college, or school viewed as an academic, social, or spiritual entity 3 : grounds that resemble a campus."
In addition to college, hospital, corporation and business campuses, it seems that the word campus can be used to describe the grounds of any set of buildings as long as the grounds are of a large enough size. Perhaps a minimum acreage should be included in the definition of campus.