Change in CPI is what CPI is, when referred to colloquially by us pilots. When it says CPI rose by 1.0% in the year June 2015 to June 2016 then it means you would get a 1% pay rise if you wanted to tie your pay to CPI.
^^^
In response to Rodney, not Snakecharma.
Note also that the things putting downward pressure on the CPI are "luxury" items such as travel and accommodation costs. So if you are a low income earner who mainly spends their money on the necessities then you may find the rise in your personal cost of living is far outstripping the CPI.