"""
A canonical link element is an HTML element that helps webmasters prevent duplicate content issues by specifying the "canonical", or "preferred", version of a web page[1][2] as part of search engine optimization. It is described in RFC 6596, which went live in April 2012.
"""

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

via http://shaarli.muges.fr/?Wd5HaA