By TheStreet Staff What Is the Russell 2,000 Stock Market Index?The Russell 2,000, also known as the “Russell 2K,” is a stock market index made up of small-cap companies. Analysts consider the Russell 2,000 to be a barometer for the financial performance of small U.S. companies. These companies are by their nature very different from the companies that make up a “headline” index like the S&P 500, which tracks some of the country’s biggest names. While investors may not be as familiar with the companies in the Russell 2,000 as they are with those in the S&P 500, when viewed together, these inde…