The Restitution

Restitution and unjust enrichment is the field of law relating to gains-based recovery. In contrast with damages (the law of compensation), restitution is a claim or remedy requiring a defendant to give up benefits wrongfully obtained. Liability for restitution is primarily governed by the "principle of unjust enrichment": A person who has been unjustly enriched at the expense of another is required to make restitution.
This principle derives from late Roman law, as stated in the Latin maxim attributed to... meer