what is the canonical url please tell me some thing about it

Canonical refers to the preferred version of a set of pages within similar pages. It helps Google know that one URL is the same a s another URL during search.

If your website opens with www & without www, then you can say it has the Canonical issue. It is not good for your website, your site should open with only one way, it would be with www or without www.

When there are two common contents in a website for different urls then the canonical urls have to be used in order to indicate to the crawlers the master page from which the content is being copied.

when any website open with www and with out www or any other url , this type of url is called canonical urls. But in the problem is that google think both the url are differet , and the benfit is also dived in both . This is called canonical issue ,It is resolved by the .htaccess file .

commented: why are you talking to yourself, omthavertch? -3

Canonical tag is use for when same website is rediret on some other URL.

Well, I think if you have done a simple Googling about What is Canonical URL I am sure you have got your answer, well anyways I am writing it over here for you

"The one authoritatively correct URL for a resource. When a resource can be accessed via multiple URLs, a canonical URL should be identified. All alias URLs for a resource should redirect to the canonical URL to enforce its authority."

all guys thanks for your kind support

We use this when there are www, non www or index.hml pages in websitejust to say google that all url is www version pages.

The canonical issue is a problem that found in the website URL when the URL open many kind like with www, without www and with index page or without index page. In this case search engine found the website URL different in every time. So this error can down the keyword rank and also effetc on the back links. So we much fix this problem by the htaccess redirection file.

Suppose http://www.abc.com and...

As a side note it's better to use www.example.com or one of the other top level DNS names that have been reserved for this purpose. You can't guarantee what any other domain might point to in the future.