Stock indices are essential tools for tracking the performance of a group of stocks, representing a sector, industry, or even the entire market. Popular examples include the S&P 500, the Dow Jones Industrial Average, and the Nasdaq Composite. These indices provide a snapshot of market trends and investor sentiment, helping traders, investors, and analysts assess the health of the broader market or specific segments. By monitoring the performance of a stock index, traders can gain insights into market movements, potential buying or selling opportunities, and risk levels.