permanent loan
noun
1A long-term financial loan without a fixed date for repayment; a sum of money lent for an indefinite period.
2(In on permanent loan) a situation in which an object is in the possession of one party (often a museum, gallery, etc.) and remains in the ownership of another, but without expectation of its return.
Origin
Mid 18th century; earliest use found in John Steuart (1676–1759).