Final answer:
An index is a single number that measures a group of stocks, such as the S&P 500.
Step-by-step explanation:
An index refers to a single number that measures a group of stocks. It provides an indication of the performance of the overall stock market or a specific sector. One popular example is the S&P 500, which consists of 500 large-cap stocks and is used as a benchmark for the overall market.
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