Imagine that the interest rate on your savings account is 1 percent a year and inflation is 2 percent a year. After one year, would the money in the account buy more than it does today, exactly the same or less than today?
The reason you have less is inflation. Inflation is the rate at which the price of goods and services rises. If the annual inflation rate is 2 percent but the savings account only earns 1 percent, the cost of goods and services has outpaced the buying power of the money in the savings account that year. Put another way, your buying power has not kept up with inflation.