A QR Code 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. [source: Wikipedia]
What makes these little babies cool is the fact that you can embed all sorts of information into a QR code, including text, phone numbers, SMS messages -- even URLs.
And that has some pretty awesome potential for webcartoonists.