A canonical URL is the “official” version of a page you want search engines to index, especially when the same or very similar content is reachable through more than one web address.
This might sound unusual, but it happens more often than you’d expect — the same product page might be accessible with and without a trailing slash, with different URL parameters, or through both HTTP and HTTPS.
Why Duplicate Content Is a Problem
Search engines don’t want to show multiple identical results for the same query. Without guidance, they might split ranking signals across duplicate URLs instead of concentrating them on one strong page, which can hurt your visibility overall.
How Canonical Tags Work
A canonical tag is added to a page’s HTML, pointing to the preferred URL. It essentially tells search engines: “if you find duplicates of this page, treat this specific address as the main one.”
Most SEO plugins for WordPress add canonical tags automatically, so you rarely need to write this by hand — but it’s worth checking, especially if your site has similar content across multiple URLs.