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.