Inflation:

Inflation is a rise in the general level of prices over time. It may also refer to a rise in the prices of a specific set of goods or services. In either case, it is measured as the percentage rate of change of a price index.
Mainstream economists believe that high rates of inflation are caused by high rates of growth of the money supply. Views on the factors that determine moderate rates of inflation are more varied: changes in inflation are sometimes attributed to fluctuations in real demand for goods and services or in available supplies (i.e. changes in scarcity), and sometimes to changes in the supply or demand for money.
There are many measures of inflation. For example, different price indices can be used to measure changes in prices that affect different people. Two widely known indices for which inflation rates are reported in many countries are the Consumer Price Index (CPI), which measures consumer prices, and the GDP deflator, which measures price variations associated with domestic production of goods and services.
A small amount of inflation can be viewed as having a beneficial effect on the economy. One reason for this is that it can be difficult to renegotiate prices and wages. With generally increasing prices it is easier for relative prices to adjust.
There are three major types of inflation, as part of what Robert J. Gordon calls the "triangle model":
• Demand-pull inflation: inflation caused by increases in aggregate demand due to increased private and government spending, etc.
• Cost-push inflation: presently termed "supply shock inflation," caused by drops in aggregate supply due to increased prices of inputs, for example. Take for instance a sudden decrease in the supply of oil, which would increase oil prices. Producers for whom oil is a part of their costs could then pass this on to consumers in the form of increased prices.
• Built-in inflation: induced by adaptive expectations, often linked to the "price/wage spiral" because it involves workers trying to keep their wages up (gross wages have to increase above the CPI rate to net to CPI after-tax) with prices and then employers passing higher costs on to consumers as higher prices as part of a "vicious circle." Built-in inflation reflects events in the past, and so might be seen as hangover inflation.
There are a number of methods that have been suggested to control inflation. High interest rates and slow growth of the money supply are the traditional ways through which central banks fight or prevent inflation, though they have different approaches.