Gross Domestic Product (GDP) refers to the final products at market prices produced by all resident units in a country during a certain period of time. Gross domestic product is expressed in three different perspectives, namely value, income, and products respectively. GDP in its value perspective refers to the balance of the total value of all goods and services produced by all resident units during a certain period of time, minus the total value of the input of goods and services of the nature of non-fixed assets; in other words, it is the sum of the value-added of all resident units. GDP from the perspective of income includes the primary income created by all resident units and distributed to resident and non-resident units. GDP from the perspective of products refers to the value of all goods and services for final demand by all resident units plus the net exports of goods and services during a given period of time. In the practice of national accounting, gross domestic product is calculated from three approaches, namely the production approach, the income approach, and the expenditure approach, which reflect the gross domestic product and its composition from different angles. For a region, it is called Gross Regional Product(GRP) or regional GDP.