According the Cornell's College of Arts and Sciences "Recognizing and Avoiding Plagiarism" tutorial, "Plagiarism is the unacknowledged use of the words or ideas of others." Often plagiarism is not recognized as such, but that doesn't help if you run of the Code of Academic Integrity!
"All of the following are considered plagiarism:
-from the "Handout on Plagiarism and Citation", originally created by Turnitin.com and modified by Medha Devare for educational use
Creative Commons "provides free tools that let authors, scientists, artists, and educators easily mark their creative work with the freedoms they want it to carry. You can use CC to change your copyright terms from "All Rights Reserved" to "Some Rights Reserved."