Image copyright Dave Coverly, Speedbump.com, 2003.
Plagiarism is using someone else's words or ideas without giving credit to the source. Many students plagiarize unintentionally, so make sure you know that plagiarism happens whenever you fail to include an in-text citation with a corresponding entry in your References or Works Cited pages. It doesn't matter if you use someone else's exact words (quote), paraphrase, or summarize: all these formats require citation. Also, citation or credit is required no matter where you find ideas or data. It doesn't matter if you're citing a peer-reviewed article, a book published by Yale University, a web site without an author, or a Tweet. All require credit. In higher education, plagiarism can lead to a failed grade or worse; in real life, it can lead to a damaged reputation or a job loss.
See our guide Academic Integrity and Avoiding Plagiarism for more detailed information.