The S&P 500 index includes the top 500 US public companies, with a focus on market capitalization.
The S&P 500 was launched in 1957 by Standard and Poor’s.
The S&P is a floating point index, which means that the market capitalization of companies in the index is governed by the number of shares available for public trading.
Due to its depth and diversity, the S&P 500 is widely considered one of the best indicators of large US stocks and even the entire stock market.
You can’t directly invest in the S&P 500 because it’s an index, but you can invest in one of the many funds that use it as a benchmark by tracking its composition and performance.