What is a rel canonical?

Hello friends,


I want to know that What is a rel canonical? tell me ...

Let’s assume you have two versions of the same page. Exactly, 100% the same content. They differ in that they’re in separate sections of your site and because of that the background color and the active menu item differ. That’s it. Both versions have been linked from other sites, the content itself is clearly valuable. Which version should a search engine show? Nobody knows.
For example’s sake, these are their URLs:

http://example.com/wordpress/seo-plugin/
http://example.com/wordpress/seo/seo-plugin/