Mutual fund. An investment company (as the term is defined in section 3 of the Investment Company Act (15 U.S.C. 80a-3)) that is an open-end company (as that term is defined in section 5 of the Investment Company Act (15 U.S.C. 80a-5)) that is registered or is required to register with the Commission under section 8 of the Investment Company Act (15 U.S.C. 80a-8).
31 CFR § 1010.100
When used in this chapter and in forms prescribed under this chapter, where not otherwise distinctly expressed or manifestly incompatible with the intent thereof, terms shall have the meanings ascribed in this subpart. Terms applicable to a particular type of financial institution or specific part or subpart of this chapter are located in that part or subpart. Terms may have different meanings in different parts or subparts.