Value of Money changes with time. This increase or decrease in the value of money over time is called the time value of money. If your money is not growing with time, it is definitely decreasing in value. Banks, the market, everything around us works on this principle.
Example:
A good example is how much the price of the same commodity such as Milk has risen in the last 5 years. You could buy 1 litre Amul milk for approximately 40 rupees but now it costs 62 rupees. Therefore, due to inflation, 40 rupees do not have enough value to buy the same amount of product as it did five years ago.