Unit investment trusts
A UIT typically issues redeemable securities, which means that the UIT will buy back an investor's units at the investor's request, and at their approximate net asset value (NAV). The UIT normally will make a one-time public offering of only a fixed number of units. It will have a termination date, and does not actively trade its investment portfolio. Furthermore, a UIT doesn't have a board of directors, corporate officers, or investment adviser to give advice during the life of the trust.
Some exchange-traded funds (ETFs) are structured as UITs. Under Securities and Exchange Commission rules, shares of ETFs are only redeemable in very large blocks (sometimes around 50,000 shares) and are traded on a secondary market.