ZIP codes are the United States specific postal code system. For other countries, the postal-code tag should be used.
ZIP codes are a system of geographically organized postal codes used by the United States Postal Service (USPS) since 1963. The basic format consists of five decimal numerical digits which locate over 40,000 postal delivery areas (which can include non-geographic areas such as ships at sea). An additional four digits ("ZIP+4") uniquely identify almost every individual postal delivery destination.
Note that ZIP codes are route designations and not necessarily geographic areas or boundaries, although they are often used as such.