A rate "lock" or "commitment" is a lender's promise to set a particular interest rate and a certain number of points for you for a specified period of time during your application process. This prevents you from going through your entire application process and discovering at the end that your interest rate has risen higher.
Although there can be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. The lending institution can agree to freeze an interest rate and points for a longer span of time, say 60 days, but in exchange, the rate (and sometimes points) will be higher than with a rate lock of fewer days.
In addition to going with a shorter rate lock period, there are several ways you are able to get the best rate. A larger down payment will result in a reduced interest rate, because you'll have more equity at the start. You can pay points to improve your rate over the life of the loan, meaning you pay more up front. For many people, this is a good option..
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