Aggregate Demand (AD) represents the total demand for all final goods and services produced in an economy at a given overall price level during a specific time period. It is the sum of all planned expenditures in the economy and is calculated as:
\[ AD = C + I + G + (X - M) \]
where C is Consumption, I is Investment, G is Government Spending, and (X - M) is Net Exports (Exports minus Imports).