Here's the basic premise:
  • Do write unique content - Search engines reward unique content.
  • Don't publish duplicate content - search engines penalise duplicate content!

Image courtesy of Images Palace

But what exactly does this mean - what is unique content and what is duplicate content? Briefly, unique content is:
  • Providing your audience with something new that they haven't read or heard before
  • Or interpreting something they have read or heard before in a different way, or providing additional value 
  • In other words, it's content which is unlike anything else on the web, has your own particular stamp or spin on things, and is remarkable or special in some way. 
Duplicate content, on the other hand, is:
  • A re-hashing of content that already exists elsewhere on the web, or on your own site
  • A re-telling of something you've read or heard before, with no extra value having been added to it
  • Or worse, straight plagiarism (copying) of something someone else has written or spoken about before, without referencing them or acknowledging them as a source
  • Or even an exact copy of another page on your site, which sometimes inadvertently happens when you have several versions of one page of content, like a print-friendly and/or mobile-friendly version of a particular page.
Rand Fishkin of Moz clearly explains the differences between unique and duplicate content in this video, published on The Moz Blog as part of their Whiteboard Friday series. Watch and learn!