When you're offered a "rate lock" from your lender, it means that you are guaranteed to keep a certain interest rate for a certain number of days for the application process. This means your interest rate cannot rise during the application process.
Although there are several lengths of rate lock periods (from 15 to 60 days), the extended spans are usually more expensive. The lender may agree to freeze an interest rate and points for a longer span of time, like 60 days, but in exchange, the rate (and sometimes points) will be more than with a rate lock of fewer days.
There are more ways to get a reduced rate, besides going with a shorter rate lock period. A bigger down payment will get you a better interest rate, because you are starting out with more equity. You could opt to pay points to improve 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 pay more up front, but you will come out ahead in the long run.
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