A more thorough explanation:

Definition: Obligatio quasi ex contractu is a legal term in Roman law that refers to an obligation that arises between two parties who have not made a contract with each other but have formed a relationship similar to a contractual one. It can also refer to a situation where a payment is made in error, creating a quasi-contractual obligation.

Example: Let's say that John hires a contractor to build a fence around his property. The contractor hires a subcontractor to do some of the work. John has no direct contract with the subcontractor, but the subcontractor performs the work and expects to be paid. In this case, there is a quasi-contractual obligation between John and the subcontractor, even though they did not directly contract with each other.

Another example of a quasi-contractual obligation is when a person receives a payment in error, such as a duplicate payment or a payment for services not rendered. The recipient of the payment has a quasi-contractual obligation to return the money to the rightful owner.

These examples illustrate how an obligation can arise between two parties who have not made a contract with each other, but have formed a relationship that creates a legal obligation similar to a contractual one.