Plagiarism occurs when

texts of third parties are taken over in whole or in part, verbatim or almost verbatim, and passed off as one's own scientific achievement. Such a procedure is not only contrary to good scientific practice, it is also a form of intellectual theft and thus a violation of copyright.

Resolution of the German University Association of July 17, 2002

Protection against plagiarism is regulated in the examination regulations. It is specified for which papers a written affirmation of the candidate is required that the examination performance was written independently, without outside help, and that no sources and aids other than those indicated were used and that quotations were marked. The affidavit, which you must sign for this purpose and enclose with the written work, can be found on the general RWTH pages in the notes on written work.

Plagiarism can be attributed to a deliberate attempt to deceive, but also to scientifically unclean work.