Plagiarism can be a confusing issue to the novice writer and even a challenging issue for more experienced writers. Cultural differences can also impact a person's expectation of what is considered acceptable.
Plagiarism is considered an breach of academic ethics and the student code of conduct and therefore your credibility as a student and as a future graduate is at risk if you fail to give this issue proper consideration. Students caught plagiarizing can be failed for an assignment, failed from a course, expelled from school and even have their diplomas revoked after graduation.
Keep in mind that plagiarism is committed any time you borrow the words or essential ideas of another person (author, student, friend or even your own documented works) without giving that person credit. There are many great resources online to help you understand plagiarism and avoid the pitfalls of plagiarism including: plagiarism.org.
This process of giving credit involves "citing your sources" and guidelines have been established by various groups to aid in the citation process. The Modern Language Association has established a set of guidelines for source citation used by many students in English classes and other disciplines. Also, the American Psychological Association has established a similar set of guidelines for students in the sciences and education.
So if you glean information from the CQ Researcher for your English paper or if you reuse portions of a paper written for your history class in your sociology class, you need to cite your sources (you might want to check with your instructor to see if they allow reusing your work from other courses). If you borrow a quote to use in your public speaking class you need to give credit to the originator of that quote both orally and in your outline or notes. In the end, any time you quote, paraphrase or borrow ideas from another person you must give the original author credit for that quote, thought or idea.