Main articles: accounting cost, opportunity cost, historical cost, marginal cost, sunk cost and transaction cost

In accounting, costs are the monetary value of expenditures for supplies, services, labor, products, equipment and other items purchased for use by a business or other accounting entity. It is the amount denoted on invoices as the price and recorded in bookkeeping records as an expense or asset cost basis.

Opportunity cost, also referred to as economic cost is the value of the best alternative that was not chosen in order to pursue the current endeavor—i.e., what could have been accomplished with the resources expended in the undertaking. It represents opportunities forgone.

In theoretical economics, cost used without qualification often means opportunity cost