marginal social cost
- The marginal cost of an activity, such as producing an additional unit of a good, where cost here includes all negative effects on society as a whole, such as negative externalities, not just the cost borne by the producer of the good. positive externalities should also be deducted.
- (written as Marginal Social Cost)The sum of marginal private cost (costs internal to the decision-maker) and marginal external costs. It is sometimes confusingly identified with the external costs, especially by non-economists.