@wikipedia



The return that could be earned per unit of time (usually one year) on an investment with similar risk, which is assumed constant over time
It is a positive number (usually designated as "") showing how future cash value  over period of time  (usually one year) is related to the present cash value :


F = P \cdot (1+r)^t


In other words it's equivalent to the interest rate in unit time  which can be potentially returned on the initial investment of cash .


The word "discount" means that a cash flow today is more valuable than identical cash flow in future because a present cash can be invested immediately and begin earning returns at rate , while a future flow cannot.


The value of discount rate is set by the corporate investment policy but usually related to the market-determined Weighted Average Cost of Capital