An ARM is an Adjustable Rate Mortgage. Unlike fixed rate mortgages that have an interest rate that remains the same for the life of the loan, the interest rate on an ARM will change periodically. The intial interest rate of an ARM is lower then that of a fixed rate mortgage, consequently, an ARM maybe a good option to consider if you plan to own your home for only a few years; you expect an increase in future earnings; or the prevailing interest rate for a fixed mortgage is to high.