a group of numbers that are used as part of an address so that post/mail can be separated into groups and delivered more quickly see also postcode Culture 'ZIP' is an abbreviation for the Zone Improvement Plan, a system introduced by the US Postal Service in 1963. The word 'zip' also suggests speed, because the numbers help mail to be delivered quickly. ZIP codes have five numbers. ZIP+4 Codes have five numbers and another four numbers separated by a hyphen, e.g. NY 10016-4314, and show a place within a certain ZIP code. compare postal district Word Origin 1960s: Zip, acronym from zone improvement plan.