What term describes a reduction in economic activity resulting in declines in output and prices?

The term that most accurately describes a reduction in economic activity leading to declines in both output and prices is deflation. Deflation occurs when there is a decrease in the overall price level of goods and services, often accompanied by a slowdown in economic activity such as reduced consumer spending and lower production levels. This phenomenon typically arises in periods of economic downturn or recession, where demand falls sharply, leading businesses to lower prices to stimulate sales.

Depreciation, on the other hand, refers to a decrease in the value of an asset over time, usually due to wear and tear or obsolescence, rather than a widespread decline in economic activity or output. Inflation is characterized by an increase in prices and a corresponding decline in purchasing power, which is the opposite of the economic conditions described in the question. Given these definitions, deflation clearly aligns with the concept of reduced economic activity resulting in a drop in output and prices.