"Imitation is the sincerest form of flattery". (Charles Caleb Colton)
Wikipedia expands on Google:
"Plagiarism is the 'wrongful appropriation' and 'stealing and publication' of another author's 'language, thoughts, ideas, or expressions' and the representation of them as one's own original work."Universities all over the world generally have explicit policies against plagiarism (the University of New South Wales and the University of Melbourne, for example) and they tend to be quite similar: the idea is that plagiarism is unethical, goes against academic integrity and honesty.
At UNSW, for instance, they give this brief additional characterization of plagiarism: "Plagiarism at UNSW is defined as using the words or ideas of others and passing them off as your own."
At the other hand, Internet post Keynesians, based abroad, are not fond of definitions and enjoy re-defining words to suit their purposes, so things might be different with them.