What is the S&P 500?
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The S&P 500 is a market-capitalization-weighted index of 500 of the largest publicly traded companies in the United States. It is one of the most widely followed benchmarks of U.S. stock market performance.
Think about a market-value-weighted index of 500 of the largest U.S. companies. It's one of the most-watched benchmarks for the U.S. stock market.