It is also the rate that the Bank of Canada targets for its monetary policy. Disinflation occurs when there is a decline in the rate of increase in prices, while deflation refers to a sustained fall in prices; where the annual change in the CPI actually turns negative year after year.
Those of you "distinguished" enough to remember the inflation of the 1970s and 1980s may wonder why anyone – particularly a central banker – might be concerned with too low a level of inflation or even a fall in the general price level. The answer is that we are not concerned if these periods are transitory.