A Media Specialist's Guide to the Internet has an explanation of what and how the QR codes work.
"QR stands for Quick Response, and is made up of black modules in a square shape on a white background.Actually, you could call it a 3D bar code. The encoded text in the square can represent a web address or text. Camera phones (with a QR app) or QR readers can read the encoded message."
The blog entry has links to ideas on using the QR code in the classroom. And QRstuff.com provides more information on the codes, a code generator and phone information.
