A good is scarce if, when it is available free,
the quantity that people want to have
is greater than the amount available.

Opportunity cost: the best alternative given up when one makes a choice.

"Voluntary" action means that there is no legal or physical restriction other than to prohibit and punish coercive harm to others.

A pure market consists of voluntary production, exchange, and consumption.

Market failure: the systematic inability of firms to provide the goods that consumers want.

An "externality" is an activity which involves uncompensated costs or benefits to others.

A tax in substance is an arbitrary cost imposed by government.

A tax in form is a payment made to government.