Inflation is a well known "Retirement Killer". Long term goals like Retirement, Children's Education, Children's Marriage, etc are highly susceptible to the ravages of inflation, since the long term nature allows for massive compounding of the ill effects of high inflation.
Cost Inflation Index is the fancy term that the Indian Income Tax Service uses to quantitatively measure inflation. This is a reasonably good measure of inflation, since the Indian government effectively chooses to waive any taxes if your investment is growing in line with the CII. There are many websites you can read up to understand how CII works. In effect it says that if your investment grew at the same pace as CII, you will not owe any taxes on the growth, since the Indian government acknowledges that your "growth" is only notional and not real.