[W]e distinguish [plagiarism] from other kinds of copying (allusion,
quotation) fairly easily: it's plagiarism if the copyist hopes no one
will notice.
-- Charles Hartman. "On Being Plagiarised"
LRB Blog (6 June 2013).
http://www.lrb.co.uk/blog/2013/06/06/charles-hartman/on-being-plagiarised/