ZIP code is a postal code system used in the United States of America by its Postal system known as the UPPS. ZIP basically means Zone Improvement Plan. The concept of ZIP code was introduced to ensure that all the mails get delivered quickly and efficiently. ZIP code primarily consists of a five digit number like 55416. These five numbers are extended after putting a hyphen by 4 numbers, which is also called as ZIP +4. For example 55416-4214.
The first digit of the ZIP code corresponds to the specific group of US states it belongs to. The second and the third digit correspond to a specific region of the group state it belongs to. Fourth and the fifth digit correspond to the delivery address group pertaining to that specific region.