An area code is a three-digit number used in telephone numbering plans to designate specific geographic regions. It helps route calls to the correct location, making it easier for phone networks to manage connections. Area codes are often associated with particular cities or regions, but they can also cover larger areas. In the United States, area codes were introduced in 1947 and are part of the North American Numbering Plan. Each area code is unique, and multiple area codes can exist within a single state. As populations grow, new area codes may be created to accommodate the increasing number of phone users.