| Term | Definition |
| Marginal Cost | The rise in total cost when output rises by 1 unit. |
| Marginal Revenue | The rise in total revenue when output raises 1 unit. |
| Monopsony | One buyer facing many sellers. |
| Externalities | One person's production or consumption physically affects the production or consuption of others. |
| Pareto Optimal | Is where a social situation, call it A, is efficient. If one cannot move from A to any other social situation, call it B, without hurting at least one person. A is optimal if, relative to any other situation b, all people are at least as well of in A as in B and no one are worse off in B than in A. |
| Monopoly | is a persistent situation where there is only one provider of a product or service in a particular market. |