Definition of 'Inflation'
The rate at which the general level of prices for goods and services is rising, and, subsequently, purchasing power is falling. Central banks attempt to stop severe inflation, along with severe deflation, in an attempt to keep the excessive growth of prices to a minimum.
Investopedia explains 'Inflation'
As inflation rises, every dollar will buy a smaller percentage of a good. For example, if the inflation rate is 2%, then a $1 pack of gum will cost $1.02 in a year.
Most countries' central banks will try to sustain an inflation rate of 2-3%.
For further reading on this subject, check out the Inflation Tutorial