The Standard & Poor's 500, often abbreviated as S&P 500, is a stock market index that measures the performance of 500 of the largest publicly traded companies in the United States. It is widely regarded as a key indicator of the overall health of the U.S. economy and stock market. The index includes companies from various sectors, such as technology, healthcare, and finance. Investors and analysts use the S&P 500 to gauge market trends and make informed investment decisions. The index is weighted by market capitalization, meaning larger companies have a greater impact on its performance. It is commonly used as a benchmark for investment portfolios.