Gross (or net) national income (at market prices) represents the total primary income to be collected by the resident institutional units: payment of employees, taxes minus subsidies towards production and imports, property income (the difference between payable and receivable income), operating surplus (gross or net) and mixed income (gross or net).
Gross national income (at market prices) is equal to GDP, minus primary income that resident institutional units must pay to non-resident institutional units, plus primary income from the rest of the world to be collected by resident institutional units.
National income is not a production concept, but rather an income concept that becomes more significant if it is expressed in net terms, i.e. once fixed capital consumption has been worked out.