Private foundation (United States)
Until 1969, the term private foundation was not defined in the United States Internal Revenue Code. Since then, every U.S. charity that qualifies under Section 501(c)(3) of the Internal Revenue Service Code as tax-exempt is a "private foundation" unless it demonstrates to the IRS that it falls into another category such as public charity.
Source: Wikipedia — Private foundation (United States) (CC BY-SA 4.0)