Plagiarism, very briefly, is taking another person's ideas and presenting them as if they are your own. Remember, the instructor thinks that anything you present (paper, project, lab report, portfolio) is your own work. Anything that is not original to you should be cited as to whose ideas they are.
Academic honesty is the academy's most cherished value.
“In support of Kent State University's standards of excellence, honesty, integrity and academic accountability, I pledge, on my honor, to conduct myself at all times in accordance with university rules that prohibit cheating, plagiarism, or any other form of academic dishonesty ... students and faculty have an ethical responsibility to ensure that the content of student work is original or cites appropriate sources for all programs at the university.”
Kent State University Honor Pledge
(Initiated by the members of the 2006-2009 Student Advisory Council of the College of Arts & Sciences)