When the yield of US debt rises, it means that the income of investors buying US debt increases, which will lead to some international funds flowing to the United States and increase the financial pressure of the United States.
When the yield of US bonds falls, it means that a lot of money is buying US bonds, because US Treasury bonds are safe assets and belong to safe assets. People will buy American bonds collectively to protect and hedge their funds, which will lead to the increase in the price of American bonds and the decrease in the yield.
Summary:
The yield of US bonds literally means the yield of US government bonds, which refers to the national bonds issued by the US Treasury on behalf of the US federal government. As for the rate of return, it is actually the ratio of annual income to total investment.