Rate Lock - A rate lock is an agreement between a borrower and a lender that guarantees a specific interest rate for a specific period of time. This ensures that the borrower will not be affected by any increases in interest rates that may occur between the time of the application and the closing of the loan. A rate lock is usually offered for a fee and can be for a specific period of time such as 15, 30, or 60 days. This type of lock helps to protect the borrower from any upward movement in the interest rates, which may cause the loan to be less affordable, but if the interest rates go down, the borrower will not benefit from the lower rates.