A service number is an identification code used to identify a person within a large group. Service numbers are most often associated with the military; however, they may be used in civilian term as well. Social Security Numbers may be seen as types of service numbers. The term "serial number" is often seen as synonym of service number; however, a serial number more accurately describes manufacture and product codes, rather than personnel identification. In the Canadian military, a "Serial Number" referred to a unique number assigned each unit that mobilized for the Second World War.