A legal doctrine requiring a person who has received a benefit at another's expense to make restitution when keeping the benefit would be unfair. It applies even when no contract exists between the parties.
From Latin 'injustus' (unjust) and 'enrichment' from Old French 'enrichir' (to make rich). The concept traces to Roman law's principle that no one should profit at another's expense without legal justification.
Unjust enrichment is the law's 'fairness police'—it doesn't care if you technically didn't break any rules; if you got richer while someone else got poorer in a way that's fundamentally unfair, you're paying it back!
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