Duplicate content – SEO WIKI
Duplicate content is non-unique materials copied from another site. They are not indexed by search engines, and this even applies, for example, to versions of a print page that have the same content as the main ones.
To avoid this, some resources host duplicate content via RSS or run the source text through synonymizer programs. Nevertheless, search robots are able to clearly identify such tricks and give authorship to the source. Often sites with duplicate content fall under a special filter, and they can be found only in additional search results. Based on this, we can conclude whether there are non-unique materials on your site.