This is a national debt. At present, there are two kinds of national debt issued in China: general national debt and special national debt. Among them, general treasury bonds, also known as national bonds, are issued with the approval of the financial department of the State Council, which are used to fill the gap of national fiscal revenue and raise funds for public facilities, important projects and other countries. Special treasury bonds are treasury bonds issued to support the development of specific fields or projects, such as fighting epidemic situation and shed reform.

According to the information you provided, "20-year 3-year bond" is a kind of national debt with a maturity of 20 years and a remaining maturity of 3 years. However, more information is needed to determine the specific type of national debt.