The iShares Russell 1000 Large-Cap Index Fund - Class K (BRGKX) is a mutual fund that seeks to track the performance of the Russell 1000 Index, which is composed of the largest 1,000 publicly traded companies in the United States. This fund is classified as a large-cap fund, meaning it primarily invests in large, well-established companies with a market capitalization of over $10 billion. As a Class K fund, it is designed for institutional investors and has a lower expense ratio compared to other share classes. This fund provides investors with a diversified portfolio of large-cap stocks, offering potential for long-term growth and stability.