Inflation is best described as:

Inflation is best defined as a rate of change in the price level, which refers to the general upward movement of prices in an economy over a period of time. It reflects how much the overall cost of goods and services is rising, resulting in a decrease in the purchasing power of money. When inflation occurs, each unit of currency buys fewer goods and services than before.

Understanding inflation primarily as a rate of change positions it in the context of economic indicators, allowing economists and policymakers to monitor its effects on the economy. It can be measured by indices such as the Consumer Price Index (CPI) or the Producer Price Index (PPI), which track the price changes of a selected set of goods and services over time.

The other options describe different economic phenomena that do not align with the fundamental nature of inflation. A decrease in the price level would describe deflation, while stagnation in economic growth refers to a period of stagnation in GDP rather than a change in prices. An increase in consumer confidence may affect economic conditions positively but does not directly describe inflation itself.