A 2D (two-dimensional) barcode is a graphical image that stores information both horizontally — as one-dimensional bar codes do — and vertically. As a result of that construction, 2D codes can store up to 7,089 characters, significantly greater storage than is possible with the 20-character capacity of a unidimensional barcode.
Sourced through Scoop.it from: searchmobilecomputing.techtarget.com
Margaret Rouse gives a great explanation on the 2D Barcode also known as QR (Quick Response) Codes. Article also includes case studies on how they have been put to use.