S&P 500

An index of 500 large U.S. companies, a key market benchmark.

The S&P 500 tracks 500 of the largest publicly traded U.S. companies, weighted by market value, and is the most widely used gauge of the U.S. stock market. Its long-term average return makes it the standard benchmark against which funds and investors measure performance.

Most years, her low-cost fund simply matched the S&P 500's return.