Definition - What does Unilateral Contract mean?
Unilateral contracts are contracts in which only one party involved has a legal obligation to fulfill the contract. The party who offers money in exchange for services rendered is typically the party who is under the legal obligation to fulfill the contract. The other party is free to choose whether or not he or she would like to perform the service in order to get the money.
Justipedia explains Unilateral Contract
Many times, people who offer money through a unilateral contract do not actually know if anyone will take their offer. For example, a person may offer a $5,000 reward for finding a missing piece of jewelry. In this case, if the reward was offered formally, then this would constitute a unilateral contract. Other parties would be free to choose to look for the jewelry or to not do so. Only a person who finds the jewelry would be entitled to reap the reward.