A type of fixed-rate mortgage, which contains a clause that entitles the borrower to reduce the fixed-interest-rate charge on the mortgage once, and early in the mortgage. The option will be exercised when interest rates fall lower then the borrowers initial mortgage rate.
There is typically a fee associated with exercising this option, and the initial mortgage might have a higher-than market-interest rate and/or high costs. However, the rate reduction option could save the borrower the costs of refinancing which might be more then the cost of using their rate improvement option.
There is no "free lunch" in the world of finance. A borrower who is told that they are being "given" the option to reduce their interest rate for a minimal fee should be aware that the lender has the true cost of that option priced in the transaction somewhere.
That's not to say the option is not fairly priced and could be valuable to the borrower should interest rates fall. The borrower should simply have a good understanding of the costs, risks and benefits of paying for the option in the initial transaction.