The total market value of all the goods and services produced within the borders of a nation during a specified period. 

The monetary value of all the finished goods and services produced within a country's borders in a specific time period, though GDP is usually calculated on an annual basis. It includes all of private and public consumption, government outlays, investments and exports less imports that occur within a defined territory.

GDP = C + G + I + NX

where:

"C" is equal to all private consumption, or consumer spending, in a nation's economy
"G" is the sum of government spending
"I" is the sum of all the country's businesses spending on capital
"NX" is the nation's total net exports, calculated as total exports minus total imports. (NX = Exports - Imports)