Duplicate content are pages at appear more than once on the internet. These identical pieces of content make it extremely problematic for search engines to determine which version of the content to use as a search engine result. Therefore the search engine is forced to choose one piece of content as the best, and this may not always be the page that was intended.
Checking for duplicate content is this essential, as the less confused a search engine robot is by your website, the faster and more favourably it will index and rank your page. If your website does contain duplicate content, it can be corrected with a 301 redirect – moving from the duplicate to the correct and original page. In fact a 301 direct can boost SEO ratings because combining pages that can be ranked will increase their relevancy.
Duplicate content can also be prevented when syndicating pages by adding a link back to the original content, or by minimizing similar content. This means combining pages that share similar features or content.
Although Google does not penalize a website for having duplicate content, it does remove pages with identical content from search results. This means that if you have two websites that contain the same content, only one of them will be displayed in the search results, and it might not be website that you want displayed. Therefore content should unique, original and never duplicated for SEO purposes.