The question describes a situation in which the supply of final goods is infinitely elastic and remains constant over a short period of time, while the aggregate output depends solely on the value of aggregate demand. This scenario leads to the determination by the principle known as the Effective demand.
In economics, the concept of 'Effective demand' refers to the idea that the output is determined by the level of demand, especially in a scenario where the supply is perfectly elastic, allowing prices to remain constant as output adjusts to variations in demand. This principle reflects Keynesian economic thought, where demand-driven factors are emphasized in determining economic outcomes.
The correct term that completes the given statement is Effective demand.