What is defined as the alternative given up when a choice is made?

The concept that describes the alternative given up when a choice is made is opportunity cost. Opportunity cost reflects the value of the next best alternative that is forgone when a decision is made. For instance, if you decide to spend your time studying for an exam instead of going out with friends, the opportunity cost would be the benefits or enjoyment you miss from that social outing.

As for other terms, a trade-off refers to the idea that in order to gain something, one must give up something else, but it doesn't specifically highlight the alternative that is sacrificed. Cost-benefit analysis is a decision-making tool that compares the benefits of an action against its costs, providing a broader evaluation of choices rather than focusing solely on the next best alternative. Value assessment is a more general process used to evaluate the worth or significance of a choice, but it doesn't explicitly address the concept of alternatives that is central to opportunity cost.