Canonical URL
The preferred URL for a piece of content when multiple URLs serve the same or similar pages, declared via `<link rel="canonical">` so search engines consolidate signals on one address.
A canonical URL is the authoritative address a site wants search engines to treat as the master copy of a page that may be reachable through duplicates (tracking parameters, http vs https, www vs apex, paginated views, regional variants). The site declares it with `<link rel="canonical" href="https://example.com/page">` in the page head, or via the `Link: <...>; rel="canonical"` HTTP header for non-HTML resources. Google may still pick a different canonical if signals conflict (sitemaps, internal links, redirects). Getting canonicalization right consolidates ranking signals on one URL instead of splintering them across duplicates.