In HTML, “rel” is an attribute associated with links. “Canonical” can be applied to the “rel” attribute, which will link to the original or authoritative page from which content is being used or referenced. The “canonical” page is the original content, and any page referencing it is a duplicate or otherwise similar page. Used to prevent duplicate content issues and maintain search engine rankings.
It is an element that prevents duplicate content issues by specifying the preferred version of a web page. In a nutshell, the rel=canonical tag tells search engines that the specific URL is the one they should look at when duplicate content is an issue.