A rate "lock" or "commitment" is a promise from the lender to lock in a specific interest rate and a particular number of points for you for a specified period during your application process. This means your interest rate cannot get higher during the application process.
Rate lock periods can vary in length, between fifteen to sixty days, with the longer spans generally costing more. The lending institution can agree to hold an interest rate and points for a longer span of time, say sixty days, but in exchange, the rate (and sometimes points) will be more than that of a rate lock of fewer days.
There are other ways to get a reduced rate, besides going with a shorter rate lock period. A larger down payment will result in a reduced interest rate, since you will be starting out with a good deal of equity. You can pay points to improve your interest rate for 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'll pay more initially, but you'll save money in the end.
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