Final answer:
The Gross Domestic Product (GDP) is the measure of an economy's size based on the value of all goods and services produced within a nation annually.
Step-by-step explanation:
The measure of an economy's size based on the market value of goods and services produced within a nation in a year is Gross Domestic Product (GDP). GDP is a key economic indicator that allows economists to gauge the health of an economy by measuring the value of all final goods and services produced within that country's borders over a specified period, usually one year. It involves the quantification of production output within the nation, multiplied by the product prices, and the summation of these values.