From Webster's Third New International Dictionary: Plagiarize - \'pla-je-,riz also j - -\ vb -rized; -riz·ing vt [plagiary] : to steal and pass off (the ideas or words of another) as one's own : use (a created production) without crediting the source vi: to commit literary theft: present as new and original an idea or product derived from an existing source.
Three Basic Varieties
Why Do Students Plagiarize?
From the University of Alberta Libraries:
How Do They Plagiarize?