It’s a concept of dividing colleges based on their need versus your desire via their marketing $$ at play to get in.. Jeff Selingo developed while researching and writing Who Gets In and Why.
The buyers are the “have-nots” in terms of admissions—although they might provide a superior undergraduate education. Rather than “select” a class, their admissions officers must work hard to recruit students and they must discount tuition through merit aid to fill classroom seats and beds in dorm rooms.
It’s best not to think of this as a scientific formula or a binary system. Rather use it as a guide in your search because most schools fall somewhere on the spectrum of buyers and sellers. For more details check out the names of the colleges on this list