Definition
What is Canonical URL?
A canonical URL is the version of a page you designate as the primary one when the same or similar content is reachable at multiple URLs. It is declared with a rel=canonical link tag in the page head. Search engines consolidate ranking signals onto the canonical and typically index it instead of the duplicates.
Why it matters
Correct canonical tags prevent duplicate-content dilution and keep search engines indexing the page you actually want to rank, protecting your organic visibility.