Plagiarism is defined as appropriating someone else's words or ideas without acknowledgment.
(Moulton, Janice, and George Robinson. "Plagiarism." Encyclopedia of Ethics, edited by Lawrence C. Becker, and Charlotte B. Becker, Routledge, 2nd edition, 2001. Credo Reference, https://bucks.idm.oclc.org/login?url=https://search.credoreference.com/content/entry/routethics/plagiarism/0?institutionId=3766. Accessed 19 Feb. 2019.)
Why talking about plagiarism is so important? You will find more information in this LibGuide prepared by another librarian Margaret Montet.