Adjusting the nominal return to compensate for factors such as inflation allows investors to determine how much of their nominal return is actually real return.
For example, let's say your bank pays you interest of 5% per year on the funds in your savings account. If the inflation rate is currently 3% per year, then the real return on your savings today would be 2%. In other words, even though the nominal rate of return on your savings is 5%, the real rate of return is only 2%, which means that the real value of your savings only increases by 2% during a one-year period.
Investment dictionary. Academic. 2012.