What is Plagiarism?
Plagiarism is any attempt to deceive others about the amount of independent work undertaken to complete an academic assignment. Extreme cases include purchasing or copying in its entirety a paper written by someone else, as well as handing in the same paper for two different classes without the instructors' permission. But it is also plagiarism to use even a single sentence (verbatim or with a little paraphrasing) from some one else's writing without formally acknowledging the source.
This definition may come as a surprise to high school students and new university students, many of whom are accustomed to writing essays by stitching together pieces of information gathered from the Internet. Writing papers in this way will get you into serious trouble in a university. Make it your goal to write everything as much as possible in your own words, and to provide footnote references every time you borrowing from someone else's work. This means you'll need to keep careful track of the sources you read while completing your assignments.
The University's stated policy is that it is your responsibility to know what plagiarism is and to avoid it in your course work. You will not escape penalty by arguing that you didn't know your behaviour constituted plagiarism. If you are in any doubt whatsoever about work that you're proposing to submit for a class, ask your instructor before you submit it.