A QR codes is a two-dimensional bar code that can be posted on or near an object so that someone with a Mobile device can snap a picture and receive additional text, media, or links related to that object.
Read more about QR codes and their implication for educators in this Educause article:
It appears that my previous web host is having technical difficulties and upgrading their server. This means some broken links for many of my projects. Aaargh! Hopefully they'll get it resolved soon, or I'll take on the huge tasks of moving sites over to a new host.