There's a lot of buzz around QR codes lately in the nonprofit community, if the nonprofit tech sites are an accurate reflection of interest. I thought I'd jump on the bandwagon.
To answer the question, "what is a QR code", it is, quite simply, a Quick Response code. There is more to this, of course. They are 2 dimensional codes that are readable by electronic means. For a better definition, visit the ever-popular Wikipedia for a definition (http://en.wikipedia.org/wiki/QR_code).