A QR-code is the most abundant form of a 2D-barcode. QR-codes can be read by e.g. smartphone apps, programs or special scanners. They can provide text information but also links to websites, e-mail adresses, telphone numbers etc.

This one:

links to the JOYCE website. If you scan it with your smart phone it will provide you the web adress http://www.geomet.uni-koeln.de/joyce/ and eventually directly direct to it. We may use it on poster and talks.

There are lots of websites which allow you to generate QR-codes. This one has been generated on http://goqr.me/de/#t=url .