Русско-англо-русский юридический словарь

In law, unjust enrichment is where one person is unjustly or by chance enriched at the expense of another, and an obligation to make restitution arises, regardless of liability for wrongdoing. A common example is when a party contracts to provide a service, but the contract is terminated prematurely due to a breach, and the contractor unjustly receives no compensation for partial services rendered.

The concept of unjust enrichment is based upon the Roman legal maxim "no one should be benefited at another's expense" (nemo locupletari potest aliena iactura or nemo locupletari debet cum alien iactura). (Wikipedia)

“Non-contractual obligations” can include tortious claims, such as negligence, misrepresentation and pre-contractual deceit or claims in respect of restitution or unjust enrichment. (lexology.com)

Unjust enrichment is a legal concept referring to situations in which one person is enriched at the expense of another in circumstances which the law treats as unjust. (Wikipedia)

In civilian systems of law, unjust enrichment is often referred to as unjustified enrichment. (Wikipedia)