Which of the following best describes a unilateral contract requirement?

A unilateral contract is characterized by a situation where only one party makes a promise that is contingent upon the action of another party. This means that one party, the offeror, is obligated to fulfill their promise once the other party, the offeree, performs a specific act. The essence of a unilateral contract lies in this one-sided promise, as the offeror is promising something in return for the performance of an act, but the offeree is not bound to act or provide anything in return unless they choose to accept the offer through their performance.

In contrast to this, a bilateral contract requires both parties to exchange promises, meaning that both are obligated to fulfill their respective promises. The requirement that contracts be in written form or need third-party approval does not define a unilateral contract; rather, these options pertain to specific requirements or conditions that may apply to contracts in general. Thus, the strength of understanding a unilateral contract is the recognition of the nature of the one-sided promise contingent on the other party's action.