A rate "lock" or "commitment" is a promise from the lender to hold a specific interest rate and a particular number of points for you for a certain period of time during your application process. This protects you from getting through your whole application process and finding out at the end that your interest rate has gone up.
While there can be a choice of rate lock periods (from 15 to 60 days), the longer ones are generally more expensive. You can get a longer period for your lock, but in doing so, will likely have a higher interest rate than you would have with a shorter rate lock period
In addition to opting for the shorter rate lock period, there are several ways you can score the lowest rate. The more the down payment, the smaller the rate will be, as you will be entering the loan with more equity. You can pay points to reduce your interest rate over the loan term, meaning you pay more up front. One strategy that is a good option for many people is to pay points to bring the rate down over the term of the loan. You will pay more up front, but you will come out ahead in the end.
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