S&P 500SPX

The S&P 500 is the most widely followed stock index in the world, tracking around 500 of the largest US public companies. It is weighted by market value, so the biggest firms move it most, and it serves as the benchmark for the US stock market and a gauge of broad economic health. You cannot buy an index directly — traders use ETFs, index funds, futures or CFDs. Its value reacts to corporate earnings, interest rates and economic data, and like any market it can fall sharply — manage risk carefully.