Camp Inch is shown to be an all-girls summer camp. Its name is printed on the girls’ uniforms, and Mrs. Inch mentions it in her speech to the girls near the beginning of the film.
It also has an “isolation cabin” called “Serendipity” by the counselors. After Susan and Sharon were caught fighting on the floor during the camp dance (and ruining it in the process), Abbey Inch, the head counselor, decided to punish them. She did so by sending them to stay at the Serendipity cabin (as well as eat at the isolation table) for the remainder of camp, so they could work out their differences. It was there that they eventually realize that they were long-lost twin sisters.