A copyright trap is a piece of erroneous or strange information which is inserted into a reference work so that copyright violations and plagiarism can be easily detected. Copyright traps are also sometimes known as fictitious entries or Mountweazels. When someone repeats the erroneous information without a proper citation, it is a sign that plagiarism or intellectual theft may have been involved, since the misinformation only exists in one place.
One classic use of the copyright trap is in maps. Map companies claim that they no longer use copyright traps, although there is some evidence to the contrary. An example of a copyright trap in a map might be a town which doesn't really exist, sometimes called a "paper town." If another mapmaker referenced the paper town in their maps, it would mean that it had stolen its information, rather than doing its own research.
Dictionaries have also been known to use copyright traps, making up words and seeing how many dictionaries fall for the trick. Dictionaries rely on original research to publish and define new words, ideally relying on several sources to confirm that the word is in common use. If a dictionary repeats a copyright trap, the original dictionary's publisher might scrutinize other entries in the dictionary closely for signs of plagiarism.
Some producers of content on the Internet also use a copyright trap to protect their content. Bloggers, for example, may insert a unique key phrase into their entries so that if another site uses their work without attribution, they can find it by looking for the key phrase. There aren't many times that a phrase like "rumpled bananas" would pop up in the middle of a web page, so these copyright traps act like fingerprints which can be used to identify lazy plagiarists who cut and paste without paying attention to the contents. These copyright traps can also act as a tip-off when material is "borrowed" for an academic paper, as the grading professor may take note of the strange phrase and research it on the Internet to find its origins.
Fictitious entries can also be humorous in nature, designed as a hoax for people with sharp eyes. The humor can sometimes backfire, however, especially if a fictitious entry is reprinted in other publications, adding an air of credibility which causes people to believe that the information is true. Confusions over birth dates, cities of birth, and other biographical information can sometimes be traced back to fictitious entries which were added as a joke and later taken seriously by people who lacked familiarity with the subject.