Definitions for "Duplicate Content"
A content copied form other web pages to increase ranking with the help of more kewords is called as duplicate content. Some search engine like Google have a filter that looks for duplicate text and thereby pushing the duplicated content deep inside the results.
separate web pages with substantially the same content, which may attract a penalty from search engines.
When two or more web pages on a single site contain the exact or significantly similar content. Some search engines including Google have filters in line to penalize sites with duplicate content when crawled therefore lowering the page rank.