What is duplicate content?

This is a term mainly used in the SEO realm of marketing. It's basically the same content, located in more than one place. Some examples: www.example.com and example.com; If both of these URL's show up when you look for a website. That website (in this case example.com) is breaking google and all Search Engine Guidelines. But typically what happens, in the Search Engines eyes, is someone is stealing someone else's content and using it as their own and trying to rank in google for work they didn't do. Called a scraper site. Duplicate content is content copied in an essentially complete form from the original publication of an original work of authorship. Duplicate content may be used to create a derivative work based on the copied content in its entirety or it may be duplicated in its original form. Examples of duplicate content could be a photocopy of an article, a Web page that appropriates the complete text of an original Web page, an unedited copy of a photograph, video or film. Duplicate content should be distinguished from fair use content, for which very limited excerpts of an original work of authorship are used in another work of authorship in a manner that does not compromise the marketable value of the original content. Duplicate content may be an authorized or unauthorized copy of original content. Authorized copies of content are arranged oftentimes through formal licensing agreements between the party who owns the rights to the original content and the party wanting to create a duplicate of that content. Unauthorized copies of content may violate either copyright laws and/or licensing agreements governing the use of original content.

Duplicate content is a key concern in online publishing today, as both authorized and unauthorized duplicate content may impact the search engine rankings of original content.

Now search engines is able to identify what is original and what is duplicate. With their improved algorithms, they are able to identify duplicate web content from original content. http://www.copyscape.com/ is another service which helps you to find duplicate content.