External cost = negative externality: cost of an activity that falls on people other than those who pursue the activity.
External benefit = positive externality: benefit of an activity received by people other than those who pursue the activity.
Externality: external cost or benefit of an activity.
Coase theorem: if at no cost people can negotiate the purchase and sale of the right to perform activities that cause externalities, they can always arrive at efficient solutions to the problems caused by externalities.
Positional externality occurs when an increase in one person's performance reduces the expected reward of another's in situations in which reward depends on relative performance.
Positional arms race: series of mutually offsetting investments in performance enhancement that is stimulated by a positional externality.
Positional arms control agreement: agreement in which contestants attempt to limit mutually offsetting investments in performance enhancement.