Duplicate content is content that appears more than once across a single website or multiple websites. For SEO marketers, duplicate content is a problem because search engines work hard to avoid displaying results with the same content on the same search.
SEO best practice can clean up duplicate content on the same website. If possible, content can be deleted. If that isn’t possible, a 301 redirect can be set up and a canonical tag can be added that points search engine bots to the original page. If a website’s content is syndicated to other websites, the source website can request canonical tags to point back to the original content.