This is the confirmation that the documents that you present are in proper form. Authentication of documents is based upon the authenticity of the original document presented to the notarizing authority e.g. the Foreign Ministry in your home country. Any translations necessary must be done from original documents. The translator must attest in their translation it has been done from an original document they received.
It must also be noted in the translation which language it was translated out of.

An Example: "This translation was done from an original document, which was in the Arabic language"

As a rule, the German Accreditation of Education Documents Agency requires all translations from overseas to be notarized and authenticated.

The legalization and/or translation of your documents are a procedure that is legally recognized by the German Embassy or the German Consultant. This legal recognition is crucial to your documents being accepted in Germany. Student applicants sometimes make the mistake of not doing this step, as a means of saving money. This, however, will lead to a lot of time and effort if the applicant tries to do this in Germany!!

NOTE: Do not forget to legalize all documents!