When I need to use canonical tag?

[RayKeller]

Hi,
I heard about this tag but to be honest I didn't know how to use it or when I should use it on my website?
what is it?

 

[elcidofaguy]

Here is a great [URLnf="http://moz.com/learn/seo/canonicalization"]article [/URLnf]which discusses canonicalization... In sum you place the <link rel="canonical" href="your website url" /> within the header of your web page...

The reason for using it is so that you can consolidate link juice to one version of that page url as search engines treat it differently..

For example with prefix www or without, with post identifier or page name etc... If these accumulate link juice with different backlinks pointing to different versions then its in your interest to consolidate it to one url format in order to improve its rankings... With that in mind I would use it always except for situations when you want to keep search engines out from indexing pages, then its not necessary...

 

[Piers Rollins]

Canonical Tag <link rel="canonical" href="your website"/> is mainly used for the purpose of avoiding page duplication issues. For example: The same page is opening for different URL's (your website, your website/index(.)html, your website/index(.)html-1, your website/index(.)html-2,...your website/index.html-99), you can use canonical tag to specify particular URL for search engine robots, bots or spiders to cache and index.