Sunk Cost is the sum that has already been incurred and cannot be recovered by any decision made now or in future. This cost is also called stranded cost. Example: A special purpose machine was bought by a company for Rs. 100000. The machine was used to make the product for which it was bought and now it is obsolete and cannot be sold. And it will be unwise to continue using that obsolete product to recover the original cost of the machine. In order words, Rs. 100000 already spent on that machine cannot be recovered in future. Such costs are said to be sunk costs and should be ignored in decision making process.