The gross domestic product, or GDP, of a country is one of the ways of measuring the size of its economy. GDP is defined as the total market value of all final goods and services produced within a given country in a given period of time (usually a calendar year). It is also considered the sum of value added at every stage of production (the intermediate stages) of all final goods and services produced within a country in a given period of time, and it is given a money value.

The most common approach to measuring and understanding GDP is the expenditure method: "Gross" means depreciation of capital stock is not subtracted. If we substitute gross investment by net investment (which is gross investment minus depreciation) in the equation above, then we obtain the formula for net domestic product. Consumption and investment in this equation are expenditure on final goods and services. The exports minus imports part of the equation (often called net exports) then adjusts this by subtracting the part of this expenditure not produced domestically (the imports), and adding back in domestic area (the exports).

Economists (since Keynes) have preferred to split the general consumption term into two parts; private consumption, and public sector (or government) spending. Two advantages of dividing total consumption this way in theoretical macroeconomics are:

• Private consumption is a central concern of welfare economics. The private investment and trade portions of the economy are ultimately directed (in mainstream economic models) to increases in long-term private consumption.
• If separated from endogenous private consumption, government consumption can be treated as exogenous, so that different government spending levels can be considered within a meaningful macroeconomic framework.