The CEFR is, as the title suggests, a framework of reference for languages.It was developed to objectively standardize language qualifications gained in different learning contexts.
It helps the learner to understand what knowledge and skills s/he should develop at each level and to measure her/his progress at each stage of learning.
The CEFR provides 'a transparent, coherent and comprehensive basis for the elaboration of language syllabuses and curriculum guidelines, the design of teaching and learning materials, and the assessment of foreign language proficiency. It is used in Europe but also in other continents.' (COE website)
The internationally recognized certificates for European languages are based on the proficiency levels of the CEFR.