National debt (national debt; Government loan, also known as national bond, is a creditor-debtor relationship formed by the state on the basis of its credit and in accordance with the general principles of debt. National debt is a bond issued by the state, a government bond issued by the central government to raise financial funds, and a debt certificate issued by the central government to investors, which promises to repay the principal and interest within a certain period of time. Because the issuer of national debt is the country, it has the highest credit and is recognized as the safest investment tool.

Rate of return refers to the rate of return on investment, generally expressed as an annual percentage, and calculated according to the current market price, face value, coupon rate and the time from the maturity date. For a company, the rate of return refers to the percentage of net profit to the average capital used.