The core idea
Inflation describes an increase in the overall price level. Your own spending basket can experience a different rate.
A little more context
Purchasing power is what money can buy. If income grows 2% and prices rise 4%, that income buys less overall.
What to remember
Disinflation is slower inflation. Deflation is a falling overall price level; these are different situations.
Pause and reflect: how would you explain this idea to someone who has never invested?