Since 1963, ZIP codes are a method of postal codes implemented by the United States Postal Service (USPS). The expression ZIP is a short form for Zone Improvement Plan. It is suitably printed in capital letters and was selected to advise that the mail goes more expeditiously, and thus more swiftly, when the dispatchers are mentioning the code in the postal address. The fundamental arrangement comprises of five decimal numeric digits. An expanded ZIP+4 code, launched in the 1980s, contains the five digits of the ZIP code, a hyphen, and four additional numbers that ascertain a more accurate position than the ZIP code only.
The expression ZIP code was initially listed as a servicemark (a category of trademark) by the USPS, however its listing has since lost validity.