In securities lending, if an investor borrows stock to short sell, they must pay interest on the funds received from selling the borrowed stock. However, the lender may agree to give a portion of this interest back to the borrower as a rebate, especially if the stock can be easily borrowed from multiple sources.
After paying off his car loan early, John received a rebate for the portion of interest he had not yet accrued, reducing his overall cost of borrowing.