A rate "lock" or "commitment" is a lender's promise to freeze a particular interest rate and a specific number of points for you for a specified period of time while your application is processed. This prevents you from going through your whole application process and learning at the end that the interest rate has risen higher.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer period usually costing more. You can get a longer period for your lock, but in choosing this option, will probably have a higher rate than you would with a shorter period
There are more ways to get a low rate, besides opting for a shorter rate lock period. A larger down payment will get you a better interest rate, since you'll have a good amount of equity from the beginning. You could opt to pay points to bring down your interest rate for the loan term, meaning you pay more initially. To many people, this makes sense and is a good deal..
Do you have a question regarding a mortgage program?