The Fidelity Series Long-Term Treasury Bond Index Fund (FTLTX) is a mutual fund that seeks to track the performance of the long-term U.S. Treasury bond market. This fund is managed by Fidelity Investments and primarily invests in a diversified portfolio of long-term Treasury bonds, providing investors with exposure to the fixed income market. With a focus on long-term bonds, this fund may offer potential for higher returns over time, but also carries a higher level of risk. FTLTX is a suitable option for investors seeking a low-cost, passive approach to investing in long-term Treasury bonds.