area of code
An area code is a three-digit number assigned to a geographical area in the United States, Canada, and the Caribbean, used before a seven-digit telephone number when placing a call to, and sometimes from within, that area. As of July 2015, there are 32 codes assigned to California. New area codes are introduced when there are no more three digit prefixes available for assignment. Once an area code no longer has any whole prefixes, it is considered to be at exhaust.