Plagiarism is using someone else's words or ideas without giving them credit. This could be a direct quote from someone without proper citation, or it could be a paraphrase of their thoughts or ideas without giving proper attribution. When in doubt, cite!
Concerns, procedures, and consequences of plagiarism are outlined in the University of Michigan Dearborn's Statement of Academic Integrity:
The University of Michigan-Dearborn values academic honesty and integrity. Each student has a responsibility to understand, accept, and comply with the University's standards of academic conduct as set forth by the Code of Academic Conduct, as well as policies established by the schools and colleges. Cheating, collusion, misconduct, fabrication, and plagiarism are considered serious offenses. Violations will not be tolerated and may result in penalties up to and including expulsion from the University.