Essentially, duplicate content is when two or more websites have the same content – not just the same subject or headers but the exact same content, word for word, reports the blog Search Engine Watch.
This may happen for several reasons, says Ron Jones, board member at Search Engine Marketing Professional Organisation (SEMPO) – a non-profit professional association working worldwide to increase awareness and promote the value of search engine marketing worldwide.
Another site or blog may have picked up an article and re-posted it, or you might have multiple sites with different domains but similar content.
However, search engines tend to filter out any duplicate content and choose one based on certain criteria. And the one that gets picked might not be yours.
To deal with the situation, Mr Jones recommends using a canonical tag, otherwise known as an authoritative page among a group of pages that have similar content.