Glossary
Canonical URL
The preferred URL of a page when multiple URLs display the same or very similar content.
Definition
A canonical URL is the 'official' or preferred version of a web page, specified using a rel='canonical' HTML link tag when multiple URLs display the same or very similar content. The canonical tag tells search engines which version to index and attribute link equity to. Without canonicalization, search engines may split ranking signals across duplicate URLs.
Why It Matters
Duplicate content is one of the most common technical SEO issues — and canonical tags are the primary solution. Without proper canonicalization, search engines may index multiple versions of the same page, splitting the backlink authority that should be concentrated on one URL.
Examples
HTTP vs HTTPShttps://example.com/page canonical points to the HTTPS version
Trailing slash variants/page/ and /page point to the same canonical URL
URL parameters/products?sort=price and /products?sort=name both canonical to /products
Common Mistakes
Self-canonicalizing to the wrong URL.
Not implementing canonicals on paginated pages.
Canonicalizing different content — canonical is for near-duplicate or exact duplicate pages.
Confusing canonical tags with redirects.