What brings a company under the Act is broader than "it calls itself a fund". Section 3(a)(1) reaches an issuer that is or holds itself out as being engaged primarily in "investing, reinvesting, or trading in securities"; an issuer in the face-amount certificate business; and, in the limb that catches people by surprise, an issuer engaged in investing, reinvesting, owning, holding or trading in securities that "owns or proposes to acquire investment securities having a value exceeding 40 per centum of the value of such issuer's total assets (exclusive of Government securities and cash items) on an unconsolidated basis". An operating business that accumulates a large securities portfolio can trip that test without ever intending to be a fund, which is why the Act carries a long list of exclusions and why structuring around it is an industry in itself.
Registered funds are subclassified again, and the second cut produces the names people actually use. Section 5 divides management companies into open-end and closed-end companies, defining an open-end company as one "offering for sale or has outstanding any redeemable security of which it is the issuer" and a closed-end company as any management company that is not open-end. It then divides both into diversified and non-diversified companies, with the diversified test requiring that at least 75 percent of total assets be represented by cash and cash items, government securities, other investment companies' securities, and other securities limited as to any one issuer to 5 percent of total assets and 10 percent of that issuer's voting securities. So "mutual fund" is not a statutory term at all: it is an open-end management company, and the statute names it that way.
What the wrapper actually buys the holder is a set of structural constraints. Four are worth stating precisely. Section 10(a) provides that no registered investment company may have a board "more than 60 per centum of the members of which are persons who are interested persons", which is the source of the independent-director requirement funds describe in their prospectuses. Section 17(a) makes it unlawful for an affiliated person, promoter or principal underwriter of a registered fund, acting as principal, knowingly to sell property to the fund or buy property from it, with narrow exceptions, which removes the most direct route for a manager to trade against the fund it runs. Section 18(f)(1) bars an open-end company from issuing senior securities at all, except that it may borrow from a bank provided that, immediately afterwards, there is "asset coverage of at least 300 per centum for all borrowings" of the company, and requires the fund to cut its borrowings back within three days, not counting Sundays and holidays, if coverage falls below that line. And section 22(e) bars a registered fund from suspending redemptions or postponing payment "for more than seven days after the tender of such security", except during a New York Stock Exchange closure or restriction, during an emergency in which the fund cannot reasonably dispose of holdings or fairly determine the value of its net assets, or for other periods the SEC permits by order.
None of that is a judgment about the investments. The SEC's own summary is worth quoting because it is the most common misunderstanding about registered funds: "It is important to remember that the Act does not permit the SEC to directly supervise the investment decisions or activities of these companies or judge the merits of their investments." The Act's protections are about structure, valuation, custody, governance and disclosure. A registered fund can lose money in an entirely lawful way, and frequently does.
The exclusions are where private funds live. Sections 3(c)(1) and 3(c)(7) take an issuer outside the definition of an investment company, the first where its securities are beneficially owned by no more than one hundred persons, or 250 for a qualifying venture capital fund, and it is not making and does not propose to make a public offering; the second where its outstanding securities are owned exclusively by qualified purchasers and, again, there is no public offering. Those two paragraphs are the legal foundation of the private-fund industry, and the trade they express is explicit: fewer investor protections in exchange for a closed door. The practical consequences belong on the pages about hedge funds and about the qualified purchaser test.