According to the Investment Company Institute, there are a number of products that mimic money market funds, but are not registered with the SEC and don’t meet the standards required to qualify as money market funds.

For example, “enhanced cash” products refer to funds that can exceed the SEC rule restrictions imposed on money market funds governing the credit quality, diversification and maturity of investments, in an effort to produce yields higher than those of a money market fund. These types of funds may only be available to sophisticated investors, institutions or government entities, and can have high minimum initial investments.

Source: Investment Company Institute