GDS stands for Großes Deutsches Sprachdiplom, set at C2+ on the European Scale of language learning.
Students taking the GDS exam should be over 18 and have 1000-1500 hours of tuition behind them. They will typically have a knowledge of specific vocabulary for particular topics, eg. technical or medical.
To hear a simple explanation and a short discussion in German, listen to the podcast:
(Press the “play” button to listen to the podcast)