Supporting organizations are public charities that carry out their exempt purposes by supporting one or more other exempt organizations, usually other public charities. Internal Revenue Service
http://www.irs.gov/charities/article/0,,id=137609,00.html

509(a)(3) supporting organizations are sub-classified as either Type I, Type II, Type III functionally integrated, or Type III non-functionally integrated organizations. After the passing of HR4 in August 2006, grants by private foundations to Type III non-functionally integrated 509(a)(3) organizations do not count as eligible distributions, and they must also be put on Expenditure Responsibility. Further information can be found at: [http://www.cof.org/Learn/content.cfm?ItemNumber=5336&navItemNumber=5337] and [http://www.cof.org/Action/content.cfm?ItemNumber=8944]