The amount of time that a lender will guarantee a loan's interest rate

Once you've locked in an interest on a loan, the lender will guarantee that rate for a certain period of time, usually for 30, 45 or 60 days (Normally, the longer the lock period, the more points that you have to pay up-front since the lender is taking a greater risk when they guarantee a rate for a long time).

You'll need to complete your home's purchase or refinance within the lock period. If you need extra time, you may have to pay up to 1 point (1% of the loan amount) or more, and there's no guarantee that you can keep your original interest rate after the expiration date.

See: Rate lock