(2) For the purpose of this section: (A) The term “endowment fund” means a fund established by State law, by an institution of higher education, or by a foundation which is exempt from taxation and is maintained for the purpose of generating income for the support of the institution, but which shall not include real estate. (B) The term “endowment fund corpus” means an amount equal to the grant or grants awarded under this section plus an amount equal to such grant or grants provided by the institution. (C) The term “endowment fund income” means an amount equal to the total value of the endowment fund established under this section minus the endowment fund corpus. (D) (i) The term “eligible institution” means an institution that is an— (I) eligible institution under part A or would be considered to be such an institution if section 1058(b)(1)(C) of this title referred to a postgraduate degree rather than a bachelor’s degree; (II) institution eligible for assistance under part B or would be considered to be such an institution if section 1063 of this title referred to a postgraduate degree rather than a baccalaureate degree; or (III) institution of higher education that makes a substantial contribution to postgraduate medical educational opportunities for minorities and the economically disadvantaged. (ii) The Secretary may waive the requirements of subclauses (I) and (II) of clause (i) with respect to a postgraduate degree in the case of any institution otherwise eligible under clause (i) for an endowment challenge grant upon determining that the institution makes a substantial contribution to medical education opportunities for minorities and the economically disadvantaged.