Overview: The Fidelity ZERO Large Cap Index mutual fund is part of the investment company’s foray into mutual funds with no expense ratio, thus its ZERO moniker.

The fund doesn’t officially track the S&P 500 — technically it follows the Fidelity U.S. Large Cap Index — but the difference is academic. The real difference is that investor-friendly Fidelity doesn’t have to cough up a licensing fee to use the S&P name, keeping costs lower for investors.