Net Present Value: This is the difference between the initial outlay or investment and the present value of the future cashflow savings for a project. This may or may not be a formal annuity since the savings in the future years is not always even (same each year). So, when the savings vary by year, it is a combination of many single sums (one for each year). But it is often a classic ...
Your discussion is 302 words gives you three examples, one accounting measure of each kind.