Plagiarism is the act of presenting someone else’s work, words, or ideas as your own. It is also called a lack of academic integrity, academic dishonesty, academic fraud, intellectual theft, and cheating.
More detailed definitions:
Florida Tech's “Simply put, plagiarism is the theft of intellectual property belonging to another. It includes the theft of unwritten ideas and concepts as well as the theft of written texts, notes, computer programs, designs, and visual materials" (Jones 4).
From: Academic Integrity & Academic Dishonesty: A Handbook About Cheating & Plagiarism - Handbook for Florida Tech students. Authored by Florida Tech's Professor Lars Jones, this handbook provides definitions and discussions of the most common types of academic dishonesty, with a focus on plagiarism.
WPA's "In an instructional setting, plagiarism occurs when a writer deliberately uses someone else’s language, ideas, or other original (not common-knowledge) material without acknowledging its source. This definition applies to texts published in print or on-line, to manuscripts, and the work of other student writers" (WPA).