A rate "lock" or "commitment" is a promise from the lender to lock in a particular interest rate and a specific number of points for you for a specified period during your application process. This means your interest rate won't grow as you are working through the application process.
Although there are various lengths of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. You can get a longer period for your lock, but in doing so, will most likely have a higher interest rate than you would with a shorter rate lock span of time
There are other ways to get a better rate, besides choosing a shorter rate lock period. A bigger down payment will result in a lower interest rate, since you'll have more equity from the beginning. You can pay points to reduce your rate over the loan term, meaning you pay more initially. To a lot of people, this makes financial sense..
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