Definitions of plagiarism
According to Carroll (2002:9) "Plagiarism is passing off someone else's work, whether intentionally or unintentionally, as your own for your own benefit".
In an instructional setting, plagiarism occurs when a writer deliberately uses someone else's language, ideas, or other original (not common-knowledge) material without acknowledging its source. (Council of Writing Programme Administrators (WPA).
Plagiarism is representing someone else's ideas, writing or other intellectual property as your own. This includes: presenting all or part of someone else's published work as something you have written; paraphrasing someone else's writing without acknowledgement; or representing someone else's artistic or technical work or creation as your own. Any use of the work of others, whether published, unpublished or posted electronically (e.g., on web sites), attributed or anonymous, must include proper acknowledgement. York University (Canada).
Plagiarism - defined as the use of any source, published or unpublished, without proper acknowledgment. Princeton
'Misuse of sources' and 'plagiarism' conflated
It is important to understand that even though you may not mean to plagiarise, it would not be right that you are given credit for work that is not your own, even if it was done in error. It is possible to be in violation of the university's rules on plagiarism because you have been careless or inadequate in the way you have cited your sources. To avoid the confusion of appearing to have plagiarised, it is better to make sure you have understood the conventions expected in citing the words and work of other people.