Plagiarism is an ethical issue because it results in someone claiming another person's work as their own without proper citation. It violates the author and his or her right for publication of their work.
There are several different types of plagiarism, and each brings its own ethical issues. In addition to copying another person's work, there is also self-plagiarism. This occurs when one duplicates their own work to be published in another location, without making note of this. In doing so, it puts the places where it was published in a difficult place because they are not offering original content. This can anger its readers and impact the quality of the publication.