The QR code (short for Quick Response code) was invented in 1994 by former Toyota subsidiary Denso Wave as a means of quickly tracking vehicles and parts through their manufacturing process. Although Denso holds the patent to QR codes, it has made the technology free for anyone to use.
QR codes are used more commonly today for logging into websites or Wi-Fi networks, sharing contacts information, making mobile payments, or storing data for plane and train tickets on your phone.
A QR code is comprised of an array of squares, some of which are used for the image sensor to position itself (that's the large squares on three of the corners), while the rest of the cells contain version and format information as well as the data itself, of course, along with error correction coding.
An early version of the two dimensional bar code system measured only 21 x 21 modules and contained just four characters of data, while the largest current version (40) spans 177 x 177 modules and can hold 1,264 characters of ASCII text or up to up to 7,089 numerals.
Interesting fact: In 2014, Heinz shipped ketchup bottles with an outdated QR code that brought customers to a porn site.