Inflation:
In economics inflation means, a rise in general level of prices of goods and services in a economy over a period of time. When the general price level rises, each unit of currency buys fewer goods and services. Thus, inflation results in loss of value of money. Another popular way of looking at inflation is "toomuch money chasing too few goods". The last definition attributes the cause of inflation to monetary growth relative to the output / availability of goods and services in the economy.
In case the price of say only one commodity rise sharply but prices of other commodities fall, it will not be termed as inflation. Similarly, in case due to rumors if the price of a commodity rise during the day itself, it will not be termed as inflation.
Deflation:
Deflation is the opposite of inflation. Deflation refers to situation, where there is decline in general price levels. Thus, deflation occurs when the inflation rate falls below 0% (or it is negative inflation rate). Deflation increases the real value of money and allows one to buy more goods with the same amount of money over time. Deflation can occur owing to reduction in the supply of money or credit. Deflation can also occur due to direct contractions in spending, either in the form of a reduction in government spending, personal spending or investment spending. Deflation has often had the side effect of increasing unemployment in an economy, since the process often leads to a lower level of demand in the economy.
Stagflation:
Stagflation refers to economic condition where economic growth is very slow or stagnant and prices are rising. The term stagflation was coined by British politician Iain Macleod, who used the phrase in his speech to parliament in 1965, when he said: “We now have the worst of both worlds - not just inflation on the one side or stagnation on the other. We have a sort of ‘stagflation’ situation.” The side effects of stagflation are increase in unemployment- accompanied by a rise in prices, or inflation. Stagflation occurs when the economy isn't growing but prices are going up. At international level, this happened during mid 1970s, when world oil prices rose dramatically, fuelling sharp inflation in developed countries.
