Google defines duplicate content as "substantive blocks of content within or across domains that either completely matches other content or is appreciably similar." But what does duplicate content mean for your site? 

Duplicate content can result in lower search rankings and decreased link popularity. The two types of duplicate content you need to be aware of are within a domain and cross-domain. 

Within a domain is the easiest to remedy, a simple 301 redirect will solve most problems. If the crawler can get to the same content through multiple paths, Google will pick one and discard the other. In this case, the best practice is picking the URL that is already indexed by Google and using a canonical tag to direct the secondary site to the primary.

Duplicate content within cross-domains are usually due to one of two reasons: content syndications or affiliates and co-brands. With syndication, Google will always show the site they think provides the most value to users within a given search, which may or may not be the version you prefer. Usually the page Google thinks provides the most value is the page with greater page authority.

When syndicating content to affiliates, there are some precautions you can take to make sure your rankings are unaffected:

  • Have the site on which your content is syndicated link back to you.
  • Have the syndicated website add a 'no index' tag.
  • Alter the syndicated content so it is not the same.
  • Make sure the main SEO elements such as URL structure and title and meta tags are different on the syndicated site and affiliate.