The postcode is a string of numerals, letters, and/or symbols officially designated by a national government or postal system which facilitates mail delivery by identifying locations systematically. If a country does not use any system of postal codes, then no postcode can be entered. Names and formats of postcodes vary from one country to the next. For example, they are called "zip codes" in the United States, and in Canada and the United Kingdom they are mixtures of numerals and letters. In certain places (including the United States), postcodes may include an optional extension for greater specificity. When the level of specificity is smaller than a particular property, then that property may not be listed with the extension. For example, if a large building houses multiple units with different postcode extensions, then the building itself should be listed without any extension.
The official locator number used by the national postal service for any address.