Canonical tag
A canonical tag (rel="canonical") is an HTML element that tells search engines which version of a page is the preferred one to index when duplicate or near-duplicate URLs exist.
Placed in the of a page, the tag points to the master URL you want ranked, for example . This consolidates signals (including link equity) onto a single URL instead of splitting them across duplicates created by tracking parameters, session IDs, or HTTP/HTTPS and www variants.
For link building, canonicals matter because a backlink pointing to a non-canonical version usually passes its value to the canonical URL Google chooses. That means a link to ?utm_source=... still benefits the clean canonical page. It is wise to ensure your important pages self-reference a clean canonical so equity does not leak.
An honest caveat: the canonical is a hint, not a directive. Google can ignore it if signals conflict (for instance, if internal links and sitemaps point elsewhere). For a hard, permanent consolidation, a redirect 301 is stronger; use canonicals when both URLs must remain accessible.