"In instructional settings, plagiarism is a multifaceted and ethically complex problem. However, if any definition of plagiarism is to be helpful to administrators, faculty, and students, it needs to be as simple and direct as possible within the context for which it is intended.
Definition: 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 to the work of other student writers." (Defining and Avoiding Plagiarism:The WPA Statement on Best Practices)
For more on plagiarism please visit Texas State University's honor code website.