What does 'quantum merit' mean?

A party who performs a valuable service for another party usually enters into a written contract or agreement before performing the service, particularly when the party is in the business of performing that service. For instance, most professional roofers hired to repair a roof insist on having a formal agreement with the owner of the house before beginning the repairs. In the absence of an agreement or formal contract, the roofer may be unable to recover losses in court if the transaction goes awry. Quantum meruit is a judicial doctrine that allows a party to recover losses in the absence of an agreement or binding contract.