Copyright infringement and plagiarism are two separate issues. Copyright is a federal law that protects original works from being copied and distributed without the author's permission, except in the case of exceptions. Plagiarism is passing off someone else's work as one's own, or with a lack of proper attribution. There is no federal or state plagiarism law but there can certainly be severe repercussions for plagiarizing.
Copyright infringement example: Incorporating an entire essay by John Updike into a published anthology without his permission. The essay should be properly attributed to Mr. Updike.
Plagiarism example: Using a line or even an entire passage by John Updike in a paper and not attributing it to the author or citing the source. This makes it seem like the passage in question is the creation of the person writing the paper and not Mr. Updike.
For more information on plagiarism, see the plagiarism guidelines available at the University of Idaho's English Department website.
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