unjust enrichment

noun

unjust en·​rich·​ment

1

: the retaining of a benefit (as money) conferred by another when principles of equity and justice call for restitution to the other party

also : the retaining of property acquired especially by fraud from another in circumstances that demand the judicial imposition of a constructive trust on behalf of those who in equity ought to receive it see also quasi contract sense 1 at contract

2

: a doctrine that requires an equitable remedy on behalf of one who has been injured by the unjust enrichment of another