What is the CEFR system?

The Common European Framework of Reference for Languages, often referred to as CEFR or CEFRL, is an international standard to describe the levels of knowledge of languages. 

There are six stages of language learning - A1, A2, B1, B2, C1, and C2. 

Source: Wikipedia

Universities often require an official certificate that proves you have C1-level in your language of study. Read more about the most commonly accepted German and English certificates.