An index, in finance, is a statistical measure that represents the performance of a specific group of assets, typically securities, stocks, or bonds, and serves as a benchmark for evaluating investment performance. Commonly known examples include the S&P 500, which tracks 500 large-cap U.S. stocks, and the Dow Jones Industrial Average, which includes 30 major American companies. Indexes can be price-weighted, market-cap weighted, or equal-weighted and are used by investors to gauge market trends, compare investment returns, and make informed decisions about asset allocation and diversification. Additionally, indexes can also represent broader economic indicators and serve as the basis for various financial products, such as index funds and exchange-traded funds (ETFs).