The Gross domestic product (GDP) is a measure of the size of a territory's economy. It is defined as the total value of all products manufactured and goods provided within that territory during a specified period (most commonly, per a year).
Contrast Gross national product (GNP), which also includes money earned by residents of the territory from overseas investment, but excludes income earned in the territory paid to residents of other territories. Increasingly, economists prefer to use GDP over GNP.
Where the territory in question is the entire planet, the GDP is called the gross world product (GWP).
GDP can be real GDP or nominal GDP; the difference is... what is the difference?.
See also Economics.