The T. Rowe Price QM U.S. Bond Index Fund Z Class (TSBZX) is a mutual fund that focuses on investing in a diverse portfolio of high-quality, investment-grade bonds issued by U.S. companies. This fund is managed by T. Rowe Price, a reputable investment management firm, and aims to track the performance of a specific bond index. The "QM" in the fund name stands for "quality mix," indicating that the fund seeks to maintain a balance between risk and return by investing in a mix of high-quality bonds. The "Z Class" designation indicates that this fund is designed for institutional investors and has lower fees compared to other share classes. Overall, TSBZX offers investors a low-cost, diversified option for investing in the U.S. bond market.