Which type of contract is defined as being contingent on an uncertain event?

An aleatory contract is accurately defined as one that is contingent on an uncertain event. This type of contract typically involves unequal exchanges where the performance of one party depends on the occurrence of a specific event, which is typically uncertain.

In the context of insurance, for example, an aleatory contract would be a policy wherein the insurer pays a benefit only if a specified event occurs, such as an accident or a loss. This uncertainty creates a situation where the outcome of the contract's terms might result in one party receiving a benefit while the other does not, based on the occurrence of an event that neither party can predict.

Bilateral and unilateral contracts differ in their obligations and how they are formed, with both typically involving certain conditions that are not based on uncertain events. A void contract, on the other hand, is one that is not enforceable by law due to various reasons, like illegality or lack of capacity, rather than being contingent on an uncertain event. Thus, the nature of an aleatory contract is unique and directly tied to the concept of uncertainty, making it the correct choice.