The rate lock might be the most complicated issue mortgage borrowers need to understand.
A rate lock is a guarantee that the lender will offer the borrower a specific combination of interest rate and points. A point is a fee or rebate equal to 1 percent of the loan amount.
Also essential to a rate lock is a time period, typically 10, 15, 30, 45 or 60 days.
A rate lock protects the borrower from rate fluctuations for the duration of the lock period. If market rates rise after the rate is locked, the borrower will still get the lower rate, to the lender's detriment.