What is Opportunity cost?
Also known as: alternative cost
The benefit that could have been obtained from the best alternative given up in order to make a particular choice. Because resources (money, time, land, labour) are limited, every decision means giving up something else; opportunity cost is the value of what was given up. It is not recorded in the accounts, since no money is paid, but it is decisive for making the right decision. It applies not only to money but also to time or any other opportunity.
Source: Britannica: Opportunity cost