National income is the total income, over a specified period of time, of all the inhabitants of an economy after allowing for capital consumption.
The term can also be used to describe a monetary flow that shows net additions to wealth. National accounting was first conducted by English economist Sir William Petty (1623-1687), and techniques were further developed during the 1930s.
Most measures of national income exclude non-market activities and certain social costs.
W Beckerman, An Introduction to National Income Analysis (London, 1966)