Value of the physical increase in stocks and work in progress
That part of the total increase in the value of stocks and work in progress which is due to changes in their quantities. This is distinguished from the part of the change in the total value of stocks and work in progress which is due to revaluations of the existing volume of stocks because of price changes. The value of the physical increase is part of the real national product, whereas the increase due to revaluation of stocks is not.
Reference: Oxford Press Dictonary of Economics, 5th edt.