English unjust enrichment law
The English law of unjust enrichment is part of the English law of obligations, along with the law of contract, tort, and trusts. The law of unjust enrichment deals with circumstances in which one person is required to make restitution of a benefit acquired at the expense of another in circumstances which are unjust.
Source: Wikipedia — English unjust enrichment law (CC BY-SA 4.0)