The correct answer is - Gross Domestic Product.
The Gross Domestic Product, or GDP, i the total dollar value of all final goods and services that have been produced in an economy in certain amount of time, usually a year.
The GDP is one of the best indicators, if not the best, about the strength of an economy, its growth, development, even its type in certain cases.
The bigger the GDP, the better the economy, and vice versa, the lower the GDP, the worse the economy. If the GDP is constantly on a rise, than we can say that the economy is growing and developing well, especially if the rise is more than 3% a year. If the GDP stagnates, or it is lowering, than the economy has big problems, as it means that it is regressing, and instead of going forward it goes backward.