Which of the following best describes gross domestic product (GDP)?

Gross domestic product (GDP) is best described as the total value of goods and services produced by a nation in a year. This definition encompasses all economic activity within a country's borders, regardless of whether that production comes from domestic or foreign entities. It includes the output of not only tangible goods such as vehicles and machinery but also intangible services such as healthcare, education, and entertainment, thus providing a comprehensive snapshot of a nation's economic performance.

In contrast, the average income of citizens in a country focuses on individual earnings rather than the overall economic output, making it a narrower measure and not reflective of total production. The total value of all goods sold in a country could imply a focus only on retail transactions, neglecting services and production activities, which are critical components of GDP. Lastly, looking solely at the sum of exports and imports of a nation relates to trade balance rather than total economic activity, which is what GDP aims to capture. Therefore, the definition that involves the total value of goods and services produced in a year best delineates the concept of GDP.