Hochschulzugangberechtigung in Deutschland?
It says it's a higher education entrance qualification in Germany.
But by higer education what does it actually mean?
Is it for bachelor's degree or master's?

Question

Answer

Normalerweise ist mit der Hochschulzugangsberechtigung der notwendige Schulabschluss nämlich das Abitur (International Baccalaureate) oder etwas Vergleichbares aus dem Ausland gemeint. Das wäre also dein koreanisches Abitur (nach dem erfolgreichen Besuch des Gymnasiums).

Answer

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.