What exactly does plagiarism mean to us? Almost every industry would have their own interpretation of plagiarism, and while there may be varying degrees to it, in essense it would be the conscious stealing of another person's thoughts and passing it off as your own. This is typically used in studies, experiments, theories and articles, but today, almost any kind of printed matter can be passed along as plagiarism.
This is not to say that you can only print words that are your own and nothing else. Remember that being able to refer to another person's thoughts or ideas is perfectly acceptable, only as long as you are acknowledging your sources. Remember that you do not always have to seek their permission to be able to print something that they wrote. All you have to do is quote the author and the book that you got it from and making sure that it did not appear like you were the one who actually wrote it.