S&P 500 Index (Standard & Poor's 500 Index)

The Standard & Poor's 500 Index, also known as the S&P 500, is a market-capitalisation-weighted index of the 500 largest publicly traded companies in the U.S. The index is widely used as a benchmark for the U.S. stock market. The index was created by Standard & Poor's, a financial services company that provides market intelligence and credit ratings, and it is now owned and managed by S&P Dow Jones Indices.

The S&P 500 includes companies from the industrial, financial, utility, and technology sectors. The S&P 500 is calculated using a market capitalisation-weighted methodology, which means that the weight of each company in the index is proportional to its market capitalisation, or the total value of its outstanding shares.

This approach ensures that larger companies have a greater impact on the index's performance than smaller companies. The index is rebalanced periodically to ensure that its composition reflects changes in the market, and the criteria for inclusion in the index are determined by a committee of market professionals.