What's Inflation?
Inflation means that the same amount of money won’t buy as much today as itcould a day or a year before (Value of money erodes with time). Inflation means a sustained increase in the aggregate or general price level in an economy. Inflation means there is an increase in the cost of living.
What's Disinflation?
Disinflation is not the same as deflation. It just means that the rate of inflation is decreasing.
For example, consider a price rise of 100 to 110 in 2017 and consider a price rise of 110 to 115 in 2018. In the year 2017 inflation was 10% while in the year 2018 inflation was around 4.6%.
See, there's inflation of 10% in 2017 while the inflation was only 4.6% in 2018. This is a disinflationary case.
What's Deflation?
Deflation on the other hand, is a fall in the price level of the economy. It means there will be a negative inflation rate.
Unlike the disinflationary case, in a deflationary scenario,
2017 price change: 100 to 110
2018 price change: 110 to 105
See, here the price itself is in a downward trend. That's Deflation.