The specific number representing "price stability" is "2 percent" in terms of the year-on-year rate of change in the CPI. For reasons why this needs to be 2 percent, I will explain three points in sequence: a bias in price statistics, securing policy room for the future, and a global standard. Let me start with a bias in price statistics.
Although I am not going into detail since this might be a bit technical, the inflation rate based on the CPI that the Bank refers to tends to be higher than actual inflation. Given this, aiming at zero inflation in terms of the CPI means aiming at negative inflation, in effect.