NPV and IRR

Net present value (NPV) and internal rate of return (IRR). Both NPV and IRR are referred to as discounted cash flow methods because they factor the time value of money into your capital investment project evaluation. Both NPV and IRR are based on a series of future payments (negative cash flow), income (positive cash flow), losses (negative cash flow), or "no-gainers" (zero cash flow).

Source: http://office.microsoft.com/en-us/excel/HA011136321033.aspx?pid=CL100570551033