A country's Gross National Product is the total value of the goods and services produced by ALL of a nation's citizens in one year. GNP is similar to GDP in that it is used as a measurement of the size of a country's economy, and GNP growth is used as a measurement of economic growth. It differs from the GDP insofar as GDP accounts only for the total value of the goods and services produced within the borders of the country, whereas GNP takes into account goods and services produced by the nations' residents overseas. Note that this may include, for example money made by an American citizen investing in the Hong Kong stock market; GDP would not account for this.
It is calculated by taking the GDP of the country, adding income earned from overseas investments by residents, and subtracting income earned within the domestic economy by overseas residents.
GNP = GDP + Overseas Income From Nation's Residents – Income Made Within Domestic Economy by Overseas Residents