Canonical URL

The same content often lives at several addresses: with and without www, over http and https, with tracking parameters such as ?utm_source=, with sort or filter options, or as a copy republished on another site. A link element with rel='canonical' in the page's head (or a Link HTTP header, for files such as PDFs) names the preferred version, so ranking signals gather on that URL and it is the one shown in results.

Google treats it as a strong hint rather than a command, weighing it alongside redirects, sitemaps and internal links, and URL Inspection in Search Console shows which version it chose. Use absolute URLs, point an original page at itself, and use a permanent (301) redirect instead when the duplicate does not need to exist at all.