The Zone Improvement Plan (ZIP) Code system is a numbered coding system which facilitates efficient mail processing. The most complete ZIP Code is a 9-digit number consisting of five digits, a hyphen, and four digits which the USPS describes as its trademark ZIP4 (see zip_four for more information). The first 5 digits, found in the zip field, represents the first 5-digit ZIP Code.
See also:
postal_code- Data Dictionaryzip_four- Data Dictionary