Net Present value, or NPV, of a Financial security is the difference between Present value of this Security and its Market value; NPV changes in the direction opposite to the change of the Discounting rate. In an Efficient market, NPVs are zero. NPV can be applied to Investment projects also. It represents the value of cash flows linked to the Investment discounted (see Discounting) at the Rate of return required by the market for the level of Risk of the Investment. Hence, NPV represents the amount of Value creation anticipated for this Investment.

(See Chapters 16 and 28 of the Vernimmen)

To know more about it, look at what we have already written on this subject