What is the "Indifference Curve" as noted in the nonfiction book, Thinking, Fast and Slow?

The “indifference curve” on a graph compares two entities that are equally desirable and share the same utility. Not giving weight to either one is the basis of the name of the comparison, the indifference curve. By not including a reference point, the scientists convince those who observe it to believe that a reference or starting point doesn’t matter. That is an unrealistic element of the indifference curve and a case of theory-based blindness. When a union negotiates for a salary increase, both sides are aware of the reference point which is the current salary. Relative to risk aversion, both sides know that they may make concessions that hurt. Risk aversion doesn’t guarantee loss; it tells the participants on both sides that it is safer to stay closer to the reference point.