What is GNP? And how it is calculated?

The Gross National Product or GNP is a measure of all of the services and goods produced outside a country over a specific period

How it is calculated?
    Gross National Product is measured as GDP plus income of residents from investments made abroad minus income earned by foreigners in domestic market.

GDP + Income of residents from investments made abroad - Income earned by foreigners in domestic market.

To measure the Country's Economic growth GDP only taken into account whereas GNP adds revenue to the Govt.