In a competitive industry we expect the industry level of production to rise or fall until marginal value (MV) equals marginal cost (MC). That is, until the value to society of one more unit is neither more nor less than the cost of the inputs required to produce that unit. If MV does not equal MC then there is a deadweight loss. Factors of the production - labor, equipment, financial capital, infrastructure, etc. - are then not being used for the most productive purpose. This situation can arise because of a production quota, restricted output by monopolists, taxes, tariffs, etc. The total consumer plus producer surplus (surplus of total value over total cost) lost to society as a result of MV being less than or greater than MC is deadweight loss. It is called a deadweight loss because it does not represent a transfer of value to someone else, as a result of a quota or other restriction, it is value that is simply lost - the total inefficiency of the restriction of MV away from MC.