area code

First three digits of a nine-digit telephone number in North American Numbering Plan, which designates a 'toll' center (geographical area that allows long-distance calling) in the US and Canada, or a specific country in the Caribbean. The first digit of an area code must be between 2 through 9, while any number could be used for second and third digit. The three digits following an area code are called the central office code or office code, and the next four digits are called the directory Number, subscriber code, or subscriber number.