What is plagiarism?
"Plagiarism is a form of academic dishonesty in which you knowingly use another person's words or ideas without giving him or her credit. Plagiarism is considered a form of theft and is a serious breach of the University Code of Conduct." ---The Temple University Writing Center
Plagiarism can also be inadvertent. If you are careless, you may be unaware that you've used someone else's words or ideas. If you haven't given credit to your source, whether you are aware of it or not, it is still plagiarism.
Learn more about plagiarism from this Temple University Writing Center handout.
How can I avoid plagiarism?
Plan ahead. Give yourself plenty of time. The closer to the deadline you wait to start working on a paper, the more likely you are to make mistakes and inadvertently plagiarize sources in your rush to completion.
Take careful notes. Make sure to indicate direct quotations.
Use quotations and paraphrasing. (Tutorial)
Use a citation manager to keep track of and organize your sources.
Develop an understanding of academic writing. They Say/I Say: The Moves That Matter In Academic Writing is an excellent introduction. If They Say/I Say: The Moves That Matter In Academic Writing is checked out, consider renting the ebook version.