A rate "lock" or "commitment" is a promise from the lender to set a certain interest rate and a specific number of points for you for a specified period of time while your application is processed. This ensures that your interest rate will not rise as you are going through the application process.
Rate lock periods can be various lengths of time, between 15 to 60 days, with the longer period generally costing more. A lending institution can agree to lock in an interest rate and points for a longer period, like sixty days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
There are more ways to get a good rate, in addition to going with a shorter rate lock period. A bigger down payment will get you a lower interest rate, because you're starting out with more equity. You can pay points to bring down your interest rate for the life of the loan, meaning you pay more up front. To many people, this is a good option..
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