Canonical URL
The one address you declare as the real home of a page, so that search engines credit it rather than splitting the value across duplicates.
Also known as canonical tag rel=canonical
Definition
The same content is often reachable at several addresses — with and without a trailing slash, with tracking parameters, filtered and unfiltered. A canonical tag says which of them counts.
Get it wrong and you compete with yourself; get it right and every link to any variant strengthens one page.
Questions about Canonical URL
Does a canonical tag stop a page being crawled?
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