The UNC Instrument of Student Judicial Governance defines plagiarism as
"deliberate or reckless representation of another's words, thoughts, or ideas as one's own without attribution in connection with submission of academic work, whether graded or otherwise." (Instrument of Student Judicial Governance, Section II.B.1)
In plain English, plagiarism means using another person’s thoughts, ideas, or written works (whether in whole or in part) and passing them off as your own. Whether you intended to plagiarize or not, if you use someone else’s work without acknowledging this through a proper citation, you are essentially stealing their work, and breaking the UNC Honor Code, as well as the principles of academic integrity.
To cite is to bring something forward as evidence. A parking ticket is sometimes called a "citation" because it points out where you parked illegally. An award can also be referred to as a "citation" because it provides evidence about what you did to deserve the prize. Citations in academic writing simply identify the source of the text (evidence) you are using.