Define and provide examples of the following term: Opportunity cost

In economics, the opportunity cost is defined as the cost of opportunity foregone. It means the cost of the next alternative given up. Simply put, it is the cost of choice.

Example: Markus has $20 saving in his pocket. He is craving to buy his favorite burger meal; however, he needs to buy some school supplies for his upcoming school fair. Markus could have bought his favorite burger meal or the school supplies he needed. What was not chosen by Markus is what cost of his choice or his opportunity cost.