Canonical URL helps to find duplicate content site by a search engine.

Search Engines use the canonical tag to combat duplicate content and assign search engine ranking value to the page designated as the "source" URL.

A canonical tag (aka "rel canonical") is a way of telling search engines that a specific URL represents the master copy of a page. Using the canonical tag prevents problems caused by identical or "duplicate" content appearing on multiple URLs.

canonical tag used to help the crawler to identify the duplicate pages.

To using canonical tags helps Google to link duplicate and similar content pages together so that Google can consolidate information under various pages under single preferred page.

It is a way of telling search engines that a specific URL represents the master copy of a page.

A canonical URL allows you to tell search engines that certain similar URLs are actually one and the same