OECD defines GDP as "an aggregate measure of production equal to the sum of the
gross values added of all resident and institutional units engaged in production (plus any taxes, and minus any subsidies, on products not included in the value of their outputs).”
IMF publication states that "GDP measures the monetary value of final goods and services - that are bought by the final user - produced in a country in a given period of time (say a quarter or a year)."
Total GDP can also be broken down into the contribution of each industry or sector of the economy.
 The ratio of GDP to the total population of the region is the
per capita GDP and the same is called Mean Standard of Living. GDP is considered the "world's most powerful statistical indicator of national development and progress"