What type of contract makes the insurer the only legally bound party to perform?

The type of contract that makes the insurer the only legally bound party to perform is a unilateral contract. In the context of insurance, this means that the insurer is obligated to pay claims or provide coverage upon the occurrence of a covered event, while the insured has the option—not a legal requirement—to fulfill their part of the contract (such as paying premiums).

In a unilateral contract, only one party—the insurer—makes a promise or commitment, whereas the other party—the insured—has the option to accept or not without becoming legally bound until they take the action of paying the premium. This is fundamental in the insurance industry, as the insurer undertakes to provide benefits in the event of a loss, while the insured's performance (e.g., payment of premiums) is conditional on their choice to maintain coverage.

In contrast, bilateral contracts involve mutual promises between two parties, where both sides are legally obligated to perform. Therefore, the essence of a unilateral contract is centered around the insurer's obligation to perform upon the insured's actions, making it distinct in its legal implications.