Opportunity Cost

Opportunity cost: is the value of the next best alternative forgone as the result of making a decision. Opportunity cost analysis is an important part of a company's decision-making processes but is not treated as an actual cost in any financial statement. The next best thing that a person can engage in is referred to as the opportunity cost of doing the best thing and ignoring the next best thing to be done.
Opportunity cost is a key concept in economics because it implies the choice between desirable, yet mutually exclusive results. It is a calculating factor used in mixed markets which favour social change in favour of purely individualistic economics. It has been described as expressing "the basic relationship between scarcity and choice."The notion of opportunity cost plays a crucial part in ensuring that scarce resources are used efficiently. Thus, opportunity costs are not restricted to monetary or financial costs: the real cost of output forgone, lost time, swag, pleasure or any other benefit that provides utility should also be considered opportunity costs.
A person who has $15 can either buy a CD or a shirt. If he buys the shirt the opportunity cost is the CD and if he buys the CD the opportunity cost is the shirt. If there are more choices than two, the opportunity cost is still only one item, never all of them.
A person who invests $10,000 in a stock denies themselves the interest that could have accrued by leaving the $10,000 in a bank account instead. The opportunity cost of the decision to invest in stock is the value of the interest.
A person who sells stock for $10,000 denies themself the opportunity to sell the stock for a higher price in the future, inheriting an opportunity cost equal to future price minus sale price.