A canonical link is a way to tell search engine robots that the page being visited is the same page, even if the page url used to access is different. Let me explain it using examples.
A search engine robot access the main page “some-site/some-page”.
Then the robot access the website archives and found “some-site/2012/11/19/some-page”.
The two links being visited are actually the same page. Note that only the url used to access is different.
We can tell the robot to index the actual page and not the archives by using canonical link. The robot will simply ignore the archives page. This helps the search engine from filling its database with duplicates data and result in faster search engine. This also helps the site by sending links to the main page, therefore increasing its popularity and ranking in the search engine. This is a win-win solution for both side.
How do you create a canonical link ? To do this, you must create a tag in the head section of the archives page. The line will look like:
<link rel=canonical href=”some-site/some-page” />
Quite simply change the text inside “href” for your main page url. That’s it. Very simple.
For further reading, you can visit Google Webmasters Help coverage by clicking the link in the references section below.