What characterizes a unilateral contract?

A unilateral contract is characterized by the presence of a promise made by only one party, where that promise is contingent upon the performance of a specific act by the other party. In this type of contract, the second party is not obligated to do anything, but if they choose to perform the act specified in the agreement, the first party is then bound to fulfill their promise.

This means that in a unilateral contract, only one side has a duty to act. For example, if someone offers a reward for the return of a lost item, the offeror makes a promise to pay the reward only if someone successfully returns the lost item. The person who finds and returns the item is not obligated to do so; they can decide whether or not to act based on their interest in claiming the reward.

The other options misunderstand the definition of a unilateral contract. A contract requiring promises from both parties describes a bilateral contract, while writing is not a requirement for all unilateral contracts, as many can be verbal. Also, involving multiple parties does not specifically define a unilateral contract, which focuses solely on the promise made by one party.