If you use the words or the ideas of another without attribution, if you copy, quote, or paraphrase (dictionaries, encyclopedias, newspapers, books, introductions, study guides, other student's papers, etc.) without proper and explicit citation, you are committing the academic crime of plagiarism.
This is academic dishonesty of the highest order.
It includes:
1) Turning in another's work as your own.
2) Use of someone else's words (a paragraph, even a sentence or phrase) without quotation marks around them (even if you provide a footnote).
3) Use of someone else's ideas (their discoveries, their original interpretations, even when paraphrased or modified) without proper and explicit citation.
If you plagiarize, you will receive an "F" for the paper and (if it is more than the matter of a sentence or two) an "F" for the course.