ICE is the abbreviation for Intercity-Express, the high-speed trains that run between the major cities in Germany.
To use the ICE you need a ticket that entitles you to do so, stating that a particular part of your journey is using such a train.
Visitors to Germany may prefer avoid using ICE trains, in order to travel the older, more scenic routes.
To hear a simple explanation in German, listen to the podcast:
(Press the “play” button to listen to the podcast)