An adjustable rate mortgage is a loan where the loan's interest rate and payment (principal and interest) change periodically.
The adjustment interval is based on the type of product that is selected at the time of application. For example a 3/1 adjustable rate mortgage has the same rate for the first three years. After that time frame the rate will adjust annually. A 5/1 adjustable rate mortgage has the same rate for the first five years. After that time frame the rate will adjust annually.