What is plagiarism?

A forthcoming article in Harper's Magazine concludes that the book, E. E. Cummings: A Biography, is plagued by plagiarism. The NY Times reports: the author "is quoted in the Harper's article as saying that he 'obviously missed some places that should have been documented' but that he 'didn't do it consciously.' Responding to a query from a reporter, he called the charge of plagiarism 'inaccurate and unfair.'" The Boston Globe reports: '''But while I clearly missed a few citations,' Sawyer-Laucanno said, ''I am not willing to admit to plagiarism.'"