A rate "lock" or "commitment" is a promise from the lender to set a specific interest rate and a particular number of points for you for a specified period of time while your application is processed. This saves you from getting through your whole application process and learning at the end that the interest rate has risen higher.
While there can be a choice of rate lock periods (from 15 to 60 days), the longer spans are typically more expensive. You can get a longer period for your lock, but in choosing this option, will probably have a higher rate than you would have with a shorter span of time
In addition to opting for the shorter rate lock period, there are several ways you are able to get the lowest rate. A larger down payment will give you a reduced interest rate, because you are starting out with a good deal of equity. You could opt to pay points to bring down your interest rate for the life of the loan, meaning you pay more initially. One strategy that is a good option for some is to pay points to bring the rate down over the life of the loan. You'll pay more initially, but you will save money, especially if you keep the loan for the full term.
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