Hello there,
For duplicate content you refer to pages that are similar or identical to each other either for content and for coding.
The crawls stats of moz will tell you exactly which pages are duplicate, but do make sure you look at every detail.
For example our domains used to be http://example.com but it has been changed to www.example.com and redirects have been used to send traffic to the new domain.
The problem I had and for some pages I still have that some pages such as delivery information, customer help as well as some products pages haven't been redirect and it is a duplicate content.
You may want to have a look also in Google Webmaster Tools to get more information but moz does an excellent job in telling you where to look.
Hope it helps.