"the appropriation or imitation of another's ideas and manner of expressing them, as in art, literature, etc., to be passed off as one's own."
-The MacQuarie Dictionary (2005)
"To represent oneself as the author of some work that is in fact the work of someone else is to plagiarize. Plagiarism may include the “passing off” of the form of the work—for example, the exact words of a piece of writing—or the intellectual content, or both."
-Encyclopedia of Social Problems (2008)
Plagiarism.org lists several common types of plagiarism: