E.164 is an international standard for telephone numbering that defines how phone numbers should be formatted and structured. It ensures that each number is unique and can be dialed from anywhere in the world. The standard specifies a maximum length of 15 digits, including a country code, which helps identify the country of the number. The country code is a prefix that indicates the nation or region, followed by a national significant number that varies in length. This system facilitates global communication by providing a consistent way to reach phone numbers across different countries and networks.