Duplicate content is all content that is available on multiple locations on or off your site. It often lives on a different URL and sometimes even on a different domain. Most duplicate content happens accidentally or is the result of a sub-par technical implementation. For instance, your site could be available on both www and non-www or HTTP and HTTPS — or both at the same time, the horror! Or maybe your CMS uses excessive dynamic URL parameters that confuse search engines. Even your AMP pages could count as duplicate content if not linked properly. Duplicate content is everywhere.