A QR code (short for Quick Response) is a specific matrix barcode (or two-dimensional code), readable by dedicated QR barcode readers and camera phones.
The code consists of black modules arranged in a square pattern on a white background. The information encoded can be text, URL or other data. QR codes storing addresses and Uniform Resource Locators (URLs) may appear in magazines, on signs, buses, business cards, or almost any object about which users might need information.
Users with a camera phone equipped with the correct reader application can scan the image of the QR code to display text, contact information, connect to a wireless network, or open a web page in the phone's browser. This act of linking from physical world objects is termed hardlinking or object hyperlinking. More info on Wikipedia.