Duplicate content is identical content that appears in more than one URL in search engines. Such content may exist because:
When you have duplicate content online, it will be difficult for search engine robots to index your content and choose one over another. To prevent showing multiple identical search results, these search engines will most likely show only one version of your content in the SERPs (search engine results pages). The final content displayed may or may not be the version you want. You don’t have to leave that up to the search engines to decide. You can have control over the content that is listed in the SERPs through proper on page optimization techniques.
Another reason to avoid having duplicate content is to not have your website appear as a spam website because of efforts to drive more traffic through content taken from other sources. Though Google has stated that they do not have a penalty for duplicate content, they aim to only list original content that has great value, and they reward these content creators in kind by ranking the content better in the SERPs.
To reduce and avoid duplicate content problems, you should:
Learn more about why you should avoid having duplicate content and using other black hat SEO techniques in today’s world of online search.