CEFR is the abbreviation of Common European Framework of Reference.
It describes what you need to be able to do in a foreign language to demonstrate mastery of that language at a certain level.
The CEFR distinguishes six levels, which can be summarized in the following diagram:
Common European Framework of Reference
A1 is the lowest level, C2 is the level of the near native speaker with an academic level. These levels can be used for all languages and mean the same thing in all countries.
The CEFR distinguishes five language skills: reading, listening, conversation, speaking and writing. These are also the skills tested in the final exams for modern foreign languages.
The CEFR is based on what you can do with those five skills in the foreign language. To determine that properly, so-called "can do descriptors" have been designed for all levels. Click here to find out what you need to be able to do to master a level.
For detailed information on the CEFR: visit the website of ERK Nederland.