From Longman Dictionary of Contemporary Englisharea codeˈarea ˌcode noun [countable] TCTnumbers you use before a phone number when you phone someone in a different area of the country
Examples from the Corpus
area code• Public meetings will be held in San Diego in November to discuss possible boundaries for the next 619 area code split.• Prefix changes Telephone customers with these prefixes have been switched to the new 760 area code.• It suggested dialing 10-321 before 1 and the area code.• And the area code showed it was in Dusseldorf - 70 miles away.• The full name and address to which the account must be paid and also its telephone number complete with area code.• Beginning tomorrow, you have to deal with area code 760. 