The iShares Russell 2000 Small-Cap Index Fund - Institutional (MASKX) is a mutual fund that seeks to track the performance of the Russell 2000 Small-Cap Index. This index represents the performance of small-cap companies in the United States. As an institutional fund, it is designed for larger investors such as pension funds, endowments, and other institutional investors. The fund provides investors with a diversified portfolio of small-cap stocks, allowing them to potentially benefit from the growth potential of smaller companies. With a focus on small-cap stocks, this fund may offer higher potential returns but also carries a higher level of risk.