The word quasi is Latin for “as if” meaning, almost alike but not perfectly alike. In law, it is used as a prefix or an adjective to inform some measure of similarity with a critical difference. A quasi-item is not an accurate example of the item, but it is close to the item minus some critical elements of the item. For example, quasi-contract, a contract implied in law or an implied-in-law contract, there is a restitution obligation implied by law or equity to prevent unjust enrichment. It is not a formal contract, but it outlines implied obligations in situations where an entity acted unilaterally to make a binding obligation toward another. In contracts, there is mutual assent between parties to produce the obligation. However, there are no consents in quasi-contracts, and the obligation arises from the law or natural equity.

Source: Legal Information Institute