The cost of
choosing one course of action over another. Letting your
second best option pass.
Economists tend to measure opportunity cost in terms of money for
simplicity's sake. However value isn't always monetary.
At the restaurant, you are presented with a desert menu. Assuming that you only eat one desert, you have the choice between
chocolate mouse, ice cream and honey
crepes. Let's say you prefer ice cream to chocolate mouse, but honey crepes are your favorite. If you eat a honey
crepe, ice cream (which would have chosen had you not had crepes) is your opportunity cost.
Another example would be if two women that you fancied, Sarah and Alice, asked you out and you said yes to Sarah (assuming monogamy), going out with Alice is your opportunity cost.