An HTML tag that helps search engines identify the original version of a web page.
Within a website, if there’s a web page that is accessible by multiple URLS or there are multiple pages with very similar content, Google considers these as duplicate versions of the original page. In such a case, a canonical tag indicates which page is original, so that Google can only index that page & display it in the results. This helps in avoiding duplicate content issues.
For example, a website might have desktop & mobile versions of the same page. Here, a canonical tag would be placed in the duplicate page & indicate the URL of the original page.
A canonical tag looks like this: . It is placed in the header of the duplicate pages.