Answer:
Opportunity cost is the measure of utility (personal satisfaction or pleasure that one derives from an action) that could have been earned or gained by choosing the alternative choice. For example, its Thursday night and your friends call you up and ask you if you want to see a movie that you really want to watch; you however have an economics test the next day that you really need to study for because you didn't really understand the unit. If you choose to go to the movies with your friends, the opportunity cost of that decision would be not gettting a good mark on your economics test. If you choose to study instead of going to the movies, the opportunity cost of that would be not being able to see that movie you wanted to watch and not being able to spend time with your friends.