Canonical URL
A canonical URL is the one address a search engine selects to represent a set of duplicate or very similar pages, and the version it shows in search results.
The same content often lives at several addresses: with and without tracking parameters, over HTTP and HTTPS or in print and mobile versions. Canonicalization is the process of picking one representative URL from that set, and Google shows only the canonical in results.
Site owners can state a preference. Google’s documentation lists permanent redirects as the strongest signal, then a rel="canonical" link element in the page head or a rel="canonical" HTTP header (useful for PDFs and other non-HTML files), then listing the preferred URL in a sitemap as a weaker signal. All of these are hints. Google may choose a different canonical if other signals disagree.
Why it matters now: reporting follows the canonical. Search Console’s Generative AI performance report assigns impressions to the canonical URL, so a muddled canonical setup splits or hides AI visibility data.
Practical note: make redirects, canonical tags, internal links and sitemaps all point to the same URL for each page.