Isn’t it just “private” school?

Independent schools are nonprofit organizations, accountable to their own governing boards, rather than to a county or state board of education. With a few exceptions (Maryland regulates the number of days all students must be in school, for example), independent schools are not bound by state regulations regarding curriculum, overall program, assigned books and other materials, athletic teams, teacher certification, and most other aspects of school governance.

Though we often use the shorthand “independent schools” as a catchall, there are many schools in other categories that are not strictly “public schools.” They include schools governed by religious organizations, such as churches (often called parochial or diocesan schools); boarding schools (schools where students live on campus); magnet programs at public schools available only by successful application; and “signature” programs available to students who already attend specific schools that offer those programs.

Most of these schools are “independent” in many ways, but most private schools prefer the term “independent,” because their self-sufficiency and independence are what most define them.