When you are offered a "rate lock" from the lender, it means that you are guaranteed to get a set interest rate for a certain number of days for your application process. This means your interest rate can't go up during the application process.
Rate lock periods can vary in length, between 15 to 60 days, with the longer period generally costing more. The lender may agree to hold an interest rate and points for a longer span of time, such as sixty days, but in exchange, the rate (and sometimes points) will be higher than with a rate lock of a shorter period.
In addition to opting for the shorter rate lock period, there are more ways you can score the lowest rate. The bigger down payment you can pay, the lower your interest rate will be, as you will have more equity from the start. You may choose to pay points to improve your interest rate over the life of the loan, meaning you pay more up front. To a lot of people, this is a good option..
Do you have a question regarding a mortgage program?