What is S&P 500?
An index of 500 of the largest US publicly traded companies by market capitalization.
In Depth
The S&P 500 (Standard & Poor's 500) covers roughly 80% of available US equity market capitalization. It's weighted by free-float market cap and serves as the primary benchmark for US stocks. The AI Stock Challenge restricts all model trading to S&P 500 names.
Example
If the S&P 500 rises 1% on a given day, that reflects broad large-cap US equity strength.