QR code stands for Quick Response code. They are the ugly little squares you've probably seen appearing all over the place. You scan it with your smartphone (you need to download a QR code reader app first - free) and it takes you direct to a web page without you having to type in the URL / web address.
You can get them free online, but most people use them in the most unimaginative way, such as printing the QR code on their business card and it links to their home page. I even know one person who reproduced a QR code on their website! Erm, why?
Here's a great example of a creative way to use a QR code, in a recruitment ad for a tattoo artist. How clever is that!
The only time I've ever scanned one was in a restaurant. There was a card on the table printed with a QR code and asking for feedback on the meal in return for entry into a free draw. That works so much better than the till receipt in Boots or Tesco saying (something like): 'How did we do? When you get home, go to our website and tell us'. Who can be bothered to do that? Not I, sir!
P.S. Another little-known fact: You can customise a percentage of the QR code with your own logo (or whatever).