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.
The picture represents the canonical url settings in medium.com (https://medium.com).Here you can enter the url of your own blog if you are
republishing the article published elsewhere on medium.com & Google or any other search engines will not penalise your blog for duplicate content & your blog will rank higher in Google Search always.
Why should you republish your articles in medium.com – It is a global professional publishing platform. Gives your article a global audience & more credibility.