Gross Domestic Product (GDP): one of the primary indicators used to gauge the health of a country's economy. It represents the total dollar value of all goods and services produced over a specific time period; you can think of it as the size of the economy. If your teacher is over 33 years old, under 54, and slightly hip, ask them this, "You down with GDP?" And about they will say, "Yeah, you know me!" Here's a great video from Planet Money about how to calculate GDP.
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The current US GDP is approximately $18.9 trillion, which is equal to 18,900,000,000,000. That's 18.9 thousand billion dollars. That's a lot!