Deflation: A decrease in the prices of goods and services, usually tied to a contraction of money in circulation. Formal deflation is measured in terms of year-to-year change.
Inflation: An increase in the prices of goods and services, usually tied to an increase of money in circulation.
Hyperinflation: Extreme inflation, minimally in excess of four-digit annual percent change, where the involved currency becomes worthless. A fairly crude definition of hyperinflation is a circumstance, where, due to extremely rapid price increases, the largest pre-hyperinflation bank note ($100 bill in the United States) becomes worth more as functional toilet paper/tissue than as currency.
