'Canonical Tag' To Help Search Engines Cut Web Clutter
< link rel="canonical" href="http://www.domain.com/original-content.html" />[close gaps]
'The canonical format provides you with more control over the URL returned in search query as it helps to make sure that properties such as link popularity are consolidated to your preferred version,' explained Joachim Kupke, Google senior software engineer, and Maile Ohye, developer programs tech lead, on the official Google Webmaster Center Blog.
The problem often associated with multiple url pointing to same source and content is that when a search engine attempts to crawl these sites, it finds all these different URLs and has to figure out which ones are most important. This is one reason many url are penalized by Search Engines.
This announcements are a signal to webmasters to start using the specialized tag to help the big search engines do a better job of indexing Web sites that have duplicate URLs (uniform resource locators) that all point to the same content. The end goal, of course, is more relevant content in front of Web searchers.