RUT refers to Russell 2000, which is a stock market index that measures the performance of 2,000 small-cap companies in the United States. The Russell 2000 is widely used by investors as a benchmark for small-cap stocks because it represents a broad range of companies across different industries and sectors. It is often used as an indicator of the health of the overall U.S. economy, as small-cap companies tend to be more closely tied to domestic economic conditions than large-cap companies.