A Canonical Link or Canonical URL is the address of a page that search engines will choose as the most relevant version of duplicate pages.

Adding the meta tag below to the <head> of a copy of a page, will tell search engines that the https://site.com/page.html address is the most relevant version.

<link rel="canonical" href="https://site.com/page.html">

Some services, like Medium, have a setting that can be used to include the Canonical URL.

A screenshot of a webpages advanced settings showing the option to customize a canonical link, along with a URL entry.