Canonical URL

A canonical URL is the version of a page a site tells search engines to treat as the primary, authoritative copy when duplicate or near-duplicate URLs exist.

Canonical tags are a strong hint, not a hard directive — Google can and sometimes does choose a different canonical than the one specified, if its own systems judge another URL to be the better representative version. Common canonicalization scenarios include URL parameter variants (tracking parameters, sort orders, session IDs), HTTP vs. HTTPS, www vs. non-www, and printer-friendly or AMP page pairs.

Getting canonicalization wrong is one of the most common causes of keyword cannibalization and split ranking signals across near-identical pages.