Extended definition
The "official" URL of a page when there are duplicate versions (e.g., with/without www, with/without trailing slash, with tracking parameters). Google uses canonical to decide which version to index.
Context and application
Canonical is just a signal, not a directive. Google can ignore your canonical if contradictory signals (internal links, sitemap, redirects) point to another page. Common mistake on paginated archives: people set canonical from /blog/page/2/ to /blog/. Wrong — page 2 is distinct content, should be self-canonical or implement rel="prev/next" (deprecated but still read by some tools). Real verification: Google Search Console “Index → Pages → Inspected URL” shows what canonical Google chose vs what you declared.
In practice
the <link rel="canonical"> tag is simple to set, but most sites get this wrong.
How SEO Master PRO MAX helps
For Canonical URL, the relevant module in the app is Audit module. See the dedicated page for how it works concretely on your site.
See Audit module →Related terms
Indexing, SEO Audit.