S&P 500
Also known as: Standard & Poor's 500
The S&P 500 is a index that tracks 500 of the largest publicly listed companies in the United States, maintained by S&P Global. It is weighted by , so the largest companies in it have far more influence over how the index moves than the smallest ones.
It is widely treated as the single best measure of the overall American , and the benchmark most professional investors are measured against. When people talk about "the market" being up or down for the day, they usually mean the S&P 500.
Because it is so closely watched, the S&P 500 is also one of the most common indexes for an or to track, giving an investor exposure to all 500 companies in a single purchase rather than needing to buy each one individually.