It's the condition to be able to enter university (Fachhochschule/Technische Hochschule/Universität), no matter what field of study or degree.
You basically must have an education comparable to what Germans learn in the Gymnasium (12/13 years of school). A school education of similar length in other countries is usually seen as equivalent. Non-native speakers may additionally need a German language qualification, but that depends on the university and the field of study.