A rate "lock" or "commitment" is a promise from the lender to set a certain interest rate and a particular number of points for you for a certain period during your application process. This keeps you from getting through your whole application process and finding out at the end that the interest rate has risen higher.
Rate lock periods can be various lengths of time, anywhere from 15 to 60 days, with the longer period usually costing more. You can get a longer period for your lock, but in making this choice, will most likely have a higher rate than you would have with a shorter span of time
There are other ways to get a better rate, besides opting for a shorter rate lock period. A larger down payment will result in a reduced interest rate, because you'll have more equity from the beginning. You can pay points to bring down your rate for the term of the loan, meaning you pay more initially. One strategy that makes financial sense for many people is to pay points to reduce the interest rate over the term of the loan. You'll pay more up front, but you will come out ahead in the end.
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