A QR code is a two-dimensional barcode, developed by Denso-Wave. QR stands for quick Response, because the code is quickly decryptable. You can scan the QR code with a mobile phone or PDA. If you have internet on your mobile phone, you can easily open the link without having to tap the address. In a similar way, email addresses, SMS messages, phone numbers and texts (up to 7089 characters) can be offered. An example code is listed below, which goes to this website. 
You can create these codes Via Google Charts API. At the very bottom of this post an online way to create a QR code using Google Charts.