S&P 500 stands for Standard & Poor's 500 which is a popular stock index that serves as bellwether of the US economy. It is an abbreviation of the Standard & Poor's 500 which denotes the current state of the US economy.
The S&P 500 Index is Standard & Poor's 500, a diverse index that includes 500 American companies that represent over 70% of the total market capitalization of the U.S. stock market.