A barcode is an optical machine-readable representation of data. It is made up of bars and spaces that vary in size. While barcodes are used in the real world, barcodes are also found in cyberspace (in the cockpit of Flynn's Recognizer) and in Space Paranoids Online.
Space Paranoids Online
In 1982, Kevin Flynn secretly put barcodes in his video game Space Paranoids. The codes, when entered into Flynn's work server, revealed Flynn's plans and sketches of his cyberspace utopia.