The Fidelity U.S. Bond Index Fund (FXNAX) is a mutual fund that seeks to track the performance of the U.S. bond market. It invests in a diverse portfolio of high-quality, investment-grade bonds issued by U.S. companies and government entities. This fund is designed to provide investors with a low-cost, passive approach to investing in the bond market, with the goal of generating steady income and preserving capital. FXNAX is managed by Fidelity Investments, a reputable and well-established financial services company.