Economic surplus: the benefit of taking an action minus its costs.
Opportunity cost: the value of the next-best alternative that must be foregone in order to undertake an activity
Sunk cost: a cost that is beyond recovery at the moment a decision must be made.
Average benefit: the total benefit of undertaking an activity divided by the units of the activity.
Average cost: the total cost of undertaking an activity divided by the units of the activity.
Marginal benefit: the extra benefit from undertaking one more unit of an activity.
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