Gross National Product (GNP)
Total output of the U.S. economy;
see the definition of Gross Domestic Product for details.
GNP and GDP tend to be used as synonyms, although GDP is definitely the preferred measure among economists and is gaining popularity in general conversation as well;
the two measures are fairly close numerically.
The difference is that GDP measures all production within the U.S., by whoever happens to be working here;
GNP measures the production of all Americans, wherever they happen to be working.
(Maybe you can remember the "N" in GNP stands for "anywhere").