Inflation is the rate at which the general price level of goods and services in an economy rises over time, which means the same amount of money buys progressively less as time passes. If inflation is running at 6% a year, something costing ₹100 today would cost roughly ₹106 a year from now, assuming that average rate holds.
Inflation matters enormously for financial planning because it silently erodes the purchasing power of money that isn't growing at least as fast as prices are rising — money sitting idle in a low-interest savings account, for instance, effectively loses real value every year. This is exactly why long-term financial goals, like retirement or a child's education, need to be planned using an inflation-adjusted future cost, rather than today's cost, and why growth-oriented investments matter for goals many years away.