1) The unrecovered balance of an investment. It's a cost already paid that is not relevant to the decision concerning the future that is being made. Capital already invested that for some reason cannot be retrieved. 2) A past cost that has no relevance with respect to future receipts and disbursements of a facility undergoing an economic study. This concept implies that since a past outlay is the same regardless of the alternative selected, it should not influence the choice between alternatives.