Section 363(m) of the Bankruptcy Code provides that the reversal or modification of an order approving a sale or lease of assets in bankruptcy does not affect the validity of the sale or lease to a good-faith purchaser or lessee unless the party challenging the sale or lease obtains a stay pending its appeal of the order. Bankruptcy and appellate courts, however, have long disagreed as to whether this provision is jurisdictional—meaning that it can never be waived and an appellate court lacks jurisdiction to hear any appeal of an unstayed sale or lease authorization order—or instead a defense that can be invoked by the proponents of the sale (e.g., the debtor, the bankruptcy trustee, or the purchaser) on appeal subject to waiver, forfeiture, and similar doctrines.