Every organization that qualifies for tax exemption as an organization described in section 501(c)(3) is a private foundation unless it falls into one of the categories specifically excluded from the definition of that term (referred to in section 509(a)). In addition, certain nonexempt charitable trusts are also treated as private foundations. Organizations that fall into the excluded categories are institutions such as hospitals or universities and those that generally have broad public support or actively function in a supporting relationship to such organizations.