This particular sample is called a QR code, but there are many other types. They can be printed, appear on a web page or email communication and can contain a web address, a text message, an email address, or up to 250 characters of text.
Software is available for most camera phones to read these codes and you can see how small a code your camera will read by downloading this handy reference. Just print the sheet out and see what your camera can read.
The first person to read this code with their phone and sends an e-mail with the contents wins a very desirable Buster Creative water bottle or stapler!