1) In layman terms, its just price rise.
2) Inflation is persistent/ sustained increase in price rise.
3) Rate of increase in the general price index prepared by authorized officials, Can be WPI,CPI,PPI.
A good definition: It is the rate by which purchasing power of the people in a particular geography has declined in a specific period.
“It is the % rate by which the prices of goods and services rise beyond their average level.”