In contract law, what is a promise to do or refrain from doing something in exchange for something else called?

In contract law, the concept you're referring to is known as consideration. Consideration is the essential element of a contract that involves a promise to do something or to refrain from doing something in exchange for something of value. It can take many forms, such as money, services, or an agreement to refrain from an action. This mutual exchange is what makes a promise enforceable by law.

While an agreement is the broader term for the mutual assent between parties, and an offer refers to the initial proposal made by one party to another, it is the presence of consideration that transforms an offer into a legally binding contract. Essentially, consideration is what incentivizes each party to enter into the agreement, establishing a reciprocal relationship that defines contractual obligations. Thus, understanding how consideration operates is fundamental to grasping the principles of contract law.