Deflation

The opposite of inflation is called deflation. It occurs when prices decline or when the rate of inflation becomes negative. However, it is not simply confined to all of prices, there is a simultaneous decline in employment, income, investment, production etc.
Inflation could be suitable in some circumstances but deflation is never desired by any economy.

Different definitions:

According to Macconal:
" Deflation is the fall in the general level of prices in the economy."

According to J.Bumol:
"Deflation refers to the sustained decline in the general price level."

According to Philips:
Deflation is a period during which level of prices decline and the value of money rises."