Which type of contract is primarily unilaterally binding?

A unilateral contract is primarily unilaterally binding because it involves an agreement where only one party makes a promise or offer, while the other party is not obligated to act but can accept the offer by performing the requested action. This means that the obligation exists only for the party making the promise until the other party fulfills the condition specified in the contract. For example, a classic scenario of a unilateral contract is a reward offer—if someone promises to pay a reward for finding a lost pet, the person who finds the pet is not required to look for it, but the offeror is obligated to pay the reward once the pet is returned.

In contrast, an implied contract is established through the actions or conduct of the parties rather than written or spoken words, meaning both parties are generally bound by mutual understandings. A joint and several contract involves multiple parties who are collectively obligated but also individually liable, meaning each party is bound to fulfill the terms, not just one. An express contract consists of terms that are clearly stated, either orally or in writing, binding both parties to the contract terms. Hence, the unilateral nature of a unilateral contract distinctly sets it apart, making it the correct choice for this question.