To plagiarize is to use someone else's work, whether published or unpublished, thru direct quotation or paraphrase, without giving credit to the author. Copy-pasting directly from the Internet or from online works is also plagiarism
Check Page 108 of Swataney (the Ship Student Handbook) f (or find on page (ctrl+F) plagiarism) or the definition of plagiarism and its repercussions.
Remember, your professor has access to plagiarism detection software.