It can really help to understand what Google or Bing means by duplicate content and its effect on SEO. Knowing this can then help you write content that ranks very high.
Search engines like Google filter out duplicate content or content which is exactly the same. The reason behind this is that they do not want searchers to see the same results twice. The first thing you need to understand is that 'content' for the sake of this article refers to unique material on your page which excludes ads, sidebars, navigation, and footers etc. The second thing you need to understand about uniqueness is that it should be both external and internal. This means that content within your own website and those from external sources need to be unique. For instance having multiple pages with the same articles is a good example of internal duplicate content. In some cases search engines will ignore internal duplication for small pieces of information. For instance there may be different versions of the page mainly because you've got a mobile version and a print version.
Referencing is not duplicate content
Many people are scared to reference specific pieces of information from sources like Wikipedia in a larger article. Some, even try not to cite a well known blog or blogger since they fear being penalized by search engines. Remember that as long as you're adding something that is unique in value referencing material does not hurt.
Unique but no value
Many people think about uniqueness in the technical sense. By taking material from other websites and just re-wording them they think that they are putting out unique material which will help them rank well. Even though the content may be unique it does not provide anything of unique value. By unique value I mean value that no other website, blog or news source has provided. And the amazing thing is that many search engines including Google are building algorithms that determine a piece of content's unique value. For instance somebody who is searching for a hotel in New York City, may also be interested in things relating to the city. They may want to know more about the weather, landmarks, culture etc., not just something which as been rewritten from Expedia's website.
Finally, it is important to talk about the treatment that low value content has been getting over the past 24 months since the Panda update was rolled out by Google. Duplicate and low quality content that exists on any one portion of your website will harm your entire site. So if you're thinking about reproducing specific sections of an article or rewording someone else's idea or even licensing articles from another place then think again. The price you pay could be at the very least be a low position in SERPs.
When you sit down to write content think about what value you're going to offer the reader. Think about if what you're writing is worth reading. Instead of getting into the technicalities of unique content you need to consider value. The more unique value you offer the better your content will perform for you.