Year 684 (DCLXXXIV) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar. The denomination 684 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Area code 684 is the number assigned to telephones in American Samoa. The area code system is part of the North American Numbering Plan, NANP.