Market Index An aggregate value produced by combining several stocks or other investment vehicles together and expressing their total values against a base value from a specific date. Market indexes are intended to represent an entire stock market and thus track the market's changes over time. Investopedia Says: Index values are useful for investors to track changes in market values over long periods of time. For example, the widely used Standard and Poor's 500 Index is computed by combining 500 large-cap U.S. stocks together into one index value. Investors can track changes in the index's value over time and use it as a benchmark against which to compare their own portfolio returns. Related Terms: Benchmark Capitalization-Weighted Index Composite Index Fundamentally Weighted Index Index Arbitrage Index Fund Portfolio Price-Weighted Index Standard & Poor's 500 Index - S&P 500 Weighted Average Market Capitalization |