Canonical URL Tag is part of the HTML header on a web page.
i<link rel="canonical" href="http://www.seopedia.wikidot.com/" />
This tag will tell search engines that the page should be treated as though it were a copy of the url www.seopedia.wikidot.com and that all of the link & content metrics the engines apply should technically flow back to that URL.
Differences with 301 redirect
- 301 redirect re-points all traffic (bots and visitors) whereas the canonical URL tag is only for search engines.
- 301 redirect is a much stronger signal that multiple pages have a single, canonical source.
- 301 redirect carry cross-domain functionality.
When you should use the canonical tag
The canonical tag should be applied when the category url system creates multiple versions of the same page.