A rate "lock" or "commitment" is a promise from the lender to hold a particular interest rate and a certain number of points for you for a specified period while your application is processed. This means your interest rate will not grow during the application process.
Rate lock periods can vary in length, anywhere from 15 to 60 days, with the longer ones generally costing more. You can get a longer period for your lock, but in doing so, will probably have a higher rate than you would have with a shorter rate lock span of time
In addition to choosing a shorter lock period, there are other ways you are able to score the best rate. The larger the down payment, the lower the interest rate will be, as you will have more equity from the start. You can pay points to lower your rate over the term of the loan, meaning you pay more up front. One strategy that makes financial sense for many people is to pay points to reduce the interest rate over the life of the loan. You are paying more up front, but you'll come out ahead, especially if you keep the loan for a long time.
Do you have a question regarding a mortgage program?