QR Codes are a form of 2D barcodes developed and popular in Japan. Found on websites, advertisements, business cards and many other things.
In the sidebar of this website you will find a QR code for each page. If you have a QR Code reader on your mobile phone you can just take a picture of the code and you will be directed to the URL you scanned the code from on your mobile device.
This is just a silly toy on a blog like this but can be good for things like your business cards, especially if you do mobile development or just want to look nerdy.