QR Code
QR is short for Quick Response (they can be read quickly by a cell phone).
They are used to take a piece of information from a transitory media and put it in to your cell phone.
You may soon see QR Codes in a magazine advert, on a billboard, a web page or even on someone's t-shirt.
Once it is in your cell phone, it may give you details about that business (allowing users to search for nearby locations), or details about the person wearing the t-shirt, show you a URL which you can click to see a trailer for a movie, or it may give you a coupon which you can use in a local outlet.