The European Council adopts in the Common European Frame of Reference for Languages the following division in six levels of proficiency
Α1: BASIC USER: Breakthrough or beginner
Α2: BASIC USER: Waystage or elementary
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Β1: INDEPENDENT USER: Threshold or intermediate
Β2: INDEPENDENT USER: Vantage or upper intermediate
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Γ1/C1: PROFICIENT USER: Effective Operational Proficiency or advanced
Γ2/C2: PROFICIENT USER: Mastery of Proficiency
See here the global description of the six levels as it is presented in the official website of the European Council (text available in 22 languages)
Global description of the six levels (Wikipedia)
KLEIS-Workshop for Greek Language and Culture follows the level-division of the European Council as it is specified for Greek by the Greek Language Centre ΚΕΓ (text available only in Greek)