Is Using An Unofficial Online Source of a Book?

Is using an unofficial online source of a book, and citing the book but not the online source, despite the fact that they have different page numbers, plagiarism?

Although I agree in part with the other answer to this question, I also strongly disagree in part. It depends on the situation. It does not completely meet the definition of plagiarism because the author authorized you to use the writing as your own. Yes, this could be ghostwriting, which is commonly done when somebody famous wants to publish a book but neither has the time or skills to write it. It is “accepted” but often the authorship is listed as by I. M. Famous with J. Nobody. On the other hand, if one turns in someone else’s writing as their own in a situation where it is required that the writing be from the attributed author, then that is a problem. If you get someone to ghostwrite your PhD dissertation, for example, that is cheating. The proper response, if found out, is to fire that person and never let them near anything where honesty and creativity are expected. Another example is the student who purchases an essay to turn in as his/her own for a college class. The original writer has given tacit permission to use the writing, but the student is violating the terms of the university, which is that it is cheating to turn in someone else’s writing as one’s own. This would be a violation of academic honesty policy and would likely result in a failure for the assignment and possible expulsion.