At the time of this posting there are almost 4,000 questions which concern duplicate content - some of these questions can be distilled to whether or not a specific practice will be qualified by Google as duplicate content.
Questions which poll for whether or not a given practice qualifies as duplicate content cannot be reasonably answered without a full accounting of Google's algorithm and are therefore not constructive, so this catch-all would be appropriate for questions of the form "is ___ duplicate content?" (as well as questions concerning the nature of duplicate content and how to correct cases where it appears as though Google is treating content as duplicated).
What is duplicate content and how can I avoid being penalized for it on my site?
What does Google consider to be duplicate content?
Will the way I am presenting my content result in a duplicate content penalty?
How can I avoid having my site's content treated as duplicate content?
Google's Duplicate Content webmaster guide defines duplicate content (for purposes of search engine optimization) as "substantive blocks of content within or across domains that either completely match other content or are appreciably similar".
Duplicate content is typically penalized (either excluded from or given a lower priority in search results) by search engines because it is often associated with scraper sites which copy content wholesale and simple article spinning techniques which generate "new" content by selectively replacing words in existing content.
Google's guide goes on to list the following as examples of duplicate content:
- Discussion forums that can generate both regular and stripped-down pages targeted at mobile devices
- Store items shown or linked via multiple distinct URLs
- Printer-only versions of web pages
Whether or not a given piece of content or technique will be considered duplicate content by a search engine is debatable without a full accounting of the algorithms used to rank and index sites, however, you can avoid penalties associated with duplicate content on your site by observing the following guidelines:
- Ensure that content is only accessible under one canonical URL
- If your site must return the same content under multiple URLs (e.g. for a "print view" page) specify a canonical URL manually with a link element in the document header
- In cases where your site returns similar content based upon parameters encoded in the URL (e.g. sorting a product catalog) exclude the URL parameters in Google Webmaster Tools
10/14 Edit: Posted to main