Mountweazels, aka fictitious entries, copyright traps, and ghost words, are deliberately incorrect entries in written and reference works such as dictionaries, encyclopedias, and maps etc. used to detect plagiarism or copyright infringement. The term was coined by The New Yorker magazine in 1975 and based on a fictitious entry for Lillian Virginia Mountweazel in the New Columbia Encyclopedia.
Other publications known to include copyright traps include The New Oxford American Dictionary, listings of the members of the German parliament, and Snopes.com (Urban Legends). Many publications run false articles around April 1 as an April Fool’s Day joke, including: Discover Magazine, Scientific American, The Economist, and others. (Wiki)