Final answer:
The opportunity cost is the value of the best alternative given up when making a decision. It is a key concept in economics that illustrates the trade-offs involved when choosing one option over others.
Step-by-step explanation:
The best alternative not selected, or the opportunity given up when making a decision, is known as the opportunity cost. For instance, if on a Friday night you choose to go to the movies over other activities like seeing a concert, volunteering at a local soup kitchen, visiting your favorite grandparent, or working at your part-time job, the best foregone alternative becomes your opportunity cost. If that best alternative happens to be visiting your favorite grandparent, then spending time with them is the opportunity cost of your decision to go to the movies. Opportunity cost varies from person to person, as each individual values alternatives differently based on their own needs and wants.