In simple terms, a quasi contract is a legal agreement that is not actually a contract, but rather an obligation imposed by the law to prevent one party from being unjustly enriched at the expense of the other. Essentially, it is a legal fiction that creates an obligation where none existed before.

Quasi contracts may arise in situations where there was no formal agreement between parties, but one party has received a benefit from the other party. For example, if a contractor agrees to build a fence for a homeowner for $500, but due to a miscommunication, the contractor builds a fence worth $1,000 and the homeowner accepts it, the contractor may be entitled to recover the additional $500. This is because the homeowner received a benefit (a fence worth $1,000) that he or she did not pay for, and the contractor did not intend to provide the benefit for free.

Quasi contracts can also arise when there is a contractual relationship between parties, but the contract is invalid or unenforceable. For example, if a car dealer sells a car to a customer, but the contract is later found to be void due to fraud or misrepresentation, the dealer may still be entitled to recover the value of the car under a quasi contract theory.

In order for a quasi contract to be enforced, certain elements must be present. First, there must be a benefit conferred upon one party by another party. Second, the party receiving the benefit must have knowledge or a reasonable expectation that the benefit will be paid for. Third, it must be shown that the party conferring the benefit did so with the expectation of payment.

Overall, quasi contracts are an important legal tool that helps to prevent unjust enrichment and ensure that parties receive the benefits they are entitled to. While they may be a bit more complicated than traditional contracts, they serve an important purpose in the world of law and business.