What is Rel=canonical?

A rel=canonical element, (also known as a canonical link or canonical tag), is a piece of HTML code which helps to prevent duplicate content issues.

rel=canonical is used in a piece of code which looks like this:

<link rel="canonical" href="www.example.com" />

This element can be placed in all versions of a webpage to tell search engines which version of a URL is the correct one to be included in the index.