This is a QR Code (otherwise known as a 2D Barcode). If you have a smart phone, there are applications you can install to view the encoded information in these tags.
You can embed hyperlinks, email addresses, contact information, and plain text into one of these. For instance, you can put your contact information into one of these and print it on a business card to make it easier to share your contact details with new clients or customers.
But the true power of one of these codes is when you use it on a print campaign. You can embed a unique hyperlink to a tracked website so you can find out how many people saw your ad. Now you can determine how many people saw your advertisement and took action without having to wait for sales figures to come back.