Define the following terms and explain their importance to the study of economics

a. public good
b. externality
c. irreversible decision
d. moral hazard
e. rent seeking

a. A public good is a commodity or service whose benefits are not depleted by an additional user, and for which it is difficult or impossible to exclude persons from its benefits.
b. An externality is an event incidental to an economic action. An externality can be beneficial or detrimental. Externalities are universal and result in (socially) non-optimal outcomes. Specifically, beneficial externalities result in under-production of goods and services, while detrimental externalities result in over-production of goods and services.
c. An irreversible decision is one in which something is permanently lost, e.g., building a dam may permanently destroy a fish species or a natural wilderness. Economists generally think that private markets alone do not handle these sorts of problems well.
d. Moral hazard refers to the tendency of insurance to discourage policyholders from protecting themselves from risk. The result can be higher insurance rates for everyone.
e. Rent seeking refers to unproductive activity in pursuit of economic profit. While producing for profit is generally desirable, rent seeking does not increase the amount of goods and services available for consumption.