Rockers are students and alumni of Simon's Rock College of Bard. Broader definitions sometimes include faculty, staff, or others closely associated with the college, and narrower ones are used to refer to those who closely fit the stereotype of a Simon's Rock student.
A Townie is any person who is not a Rocker. It is typically only used to refer to residents of Great Barrington, MA, but in the most general sense can mean all people who are not part of the college. Similar to the more narrow definitions of "Rocker," the term "Townie" can be used to refer specifically to those residents of Great Barrington that closely fit the Townie stereotype, and generally denotes sketchiness. Townies are not allowed on campus after midnight unless they have checked in to stay with a student overnight (this can be done at the Security Shack).
Rockers and Townies form a mutually exclusive bipartition, with the exception of day students, who are able to simultaneously exist as both Rockers and Townies, something that can be extremely difficult at times.