Plagiarism is using the work of others and pretending it is your own. The Merriam Webster Dictionary defines plagiarizing as "to steal and pass off (the ideas or words of another) as one's own" (emphasis mine).
It is plagiarism if you copy someone else's words without giving them credit.
It is plagiarism if you make only light cosmetic changes to someone else's words, such as using a synonym.
Your professors want to see your work--not someone else's. This is your grade, so it needs to be your work.
You will not receive credit for the work you turned in if it contained plagiarism. If your plagiarism is severe and/ or you do it multiple times you can be expelled from the program and/ or university.
This video is created by Kevin deLaPlante on March, 2010. This is a sample video from a video tutorial course titled "How to Cite Sources and Avoid Plagiarism". You can find this and other tutorial courses at http://www.criticalthinkingtutorials.com.