GSM stands for Global System for Mobile communications and is the the mobile phone standard common in many parts of the world. It has been the main standard in Germany since the middle of the 1990s.
The two GSM frequencies in Germany are known as D-Netz and E-Netz.
The standard also covers features such as SMS (Kurznachrichten), which started out as a by-product and is now one of the most popular ways of using a mobile phone.
To hear a simple explanation and a short discussion in German, listen to the podcast:
(Press the “play” button to listen to the podcast)