According to Wikipedia, car sharing is "a system where a fleet of cars (or other vehicles) is owned and operated/overseen by a company, public agency, cooperative, ad hoc grouping, or even a single individual, and made available for use by members of the carshare group in a wide variety of ways." In the fall of 2006, Zipcar expanded to include the University of Rochester as one of its service locations.
Since then, the program has been opened to include any member of Zipcar, not just people affiliated with the University of Rochester.