Unintentional plagiarism can be defined as plagiarism that occurs without the student meaning to plagiarize or knowing that he or she is plagiarizing. This sort of plagiarism typically happens when students do not know the rules about citing sources.
Unintentional plagiarism typically occurs when a student copies only a few words from a passage or when they take an idea from someone else. In each case, it is necessary to give credit to the author from whom the words or the idea were taken.
Unintentional plagiarism, then, is plagiarism that occurs because of ignorance of the rules, not because of an intent to plagiarize.