Measuring the Health of the Economy
One purpose of an economy is to provide people with goods and services – cars, computers, video games, houses, rock concerts, fast food, amusement parks. One way in which economists measure the performance of an economy is by looking at a widely used measure of total output called gross domestic product (GDP). GDP is defined as the market value of all goods and services produced by the economy in a given year. In the United States, it's calculated by the Department of Commerce. GDP includes only those goods and services produced domestically; goods produced outside the country are excluded. GDP also includes only those goods and services that are produced for the final user; intermediate products are excluded. For example, the silicon chip that goes into a computer (an intermediate product) would not count, even though the finished computer would.
By itself, GDP doesn't necessarily tell us much about the state of the economy. But& change in GDP does. If GDP (after adjusting for inflation) goes up, the economy is growing. If it goes down, the economy is contracting.