Duplicate content refers to content that appears online in more than one place. By “place,” we mean a page with a unique URL. It can be exactly the same content or almost exactly the same, and it can be on the same website or on another site.
You may not get penalized — technically — by Google for duplicate content, but it can hurt your search engine ranking. That’s because it’s hard for search engines to figure out which location of the content is the most relevant. As a result, none of the URLs end up ranking highly, and no single page gets the highest possible search visibility.
Google is supposed to be able to detect duplicate content, group all of the URLs into one cluster, and then choose the best result. But this doesn’t always work correctly, and the wrong URL may be chosen. Ultimately, website owners may notice lower rankings or reduced traffic due to duplicate content. Luckily, there are ways to prevent this sort of thing from happening to your sites.