What is canonical URL?

I am new to this SEO world. I want to know about canonical URL, where to use it. And how it helps in SEO.

Take a look at this thread: http://www.sitepoint.com/forums/showthread.php?t=699789&highlight=canonical

In the future, before you post, please Search using the vBulletin Advanced Search and SitePoint’s [URL=“http://search.sitepoint.com/”]Advanced Search

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