Academic integrity and honesty is an important demand that the academic community imposes on its members. Integrity is crucial in several scientific activities and on different moments:
In research and publishing:
Scientists feel an increasing pressure from society to stick to these rules. Being fully independent or at least the indicating clearly any competing interest and interests of third parties is crucial to the credibility and use of scientific findings. These rules of conduct apply to all members of the scientific community, including students.
There are also various codes of conduct to which researchers and students must abide. You can find these at:
Plagiarism is reusing material without giving the source
Within the law and according to citation rights you are allowed to cite texts without it being seen as plagiarism. However, if you do so without stating the source, you breach the codes of conduct in the academic community.
Why is plagiarism so harmful? There are several reasons:
There are many aspects to plagiarism:
Combinations of all of these aspect result in hundreds of ways to commit plagiarism. Some rarely occur, others frequently. Some are more serious than others.
Some forms have a name of their own, such as self plagiarism for sections taken over without stating the source of which you yourself are (co)-author of the original text. If you are the only author of the original, reasons 1 & 2 mentioned above are not important, but reasons 3 & 4 still make it into a serious offence. If you are co-author, all four reasons turn it into culpable behaviour.
Some forms are still objectionable, even if references are included, for instance if you include or paraphrase large sections or if these take up a large part of the new publication (in terms of size or importance).
There are also offences which are not related to plagiarism, but are serious nevertheless, such as excessive self-citation, not for reasons of improving the text but only because you want to raise your citation scores.