The issue of duplicate content is something vague even for the most well-seasoned internet marketers. There are two different views on the rules for duplicate content—one where anything that has been previously published should not be put-up anywhere again; and the other is that the same texts can be used as long as not for the same website.
Google algorithm for search results is among the biggest secrets that a lot of SEO experts have been trying to break for the longest time. And among the grey areas that has not yet been exactly defined is the scope of duplicate content, especially with the search engines particularly reserved about the issue. However, as uncommunicative as they are, they are also quick to penalize websites that steps over the boundaries and commit such repetition of content use.
One strategy that has worked for most websites is the prevention of using the same article for every page without changing anything in them. But aside from triggering the duplicate content penalty, you will also be stripping the site off of credibility if anyone happens to come by and browse through the pages just to read the same article.
No matter how anyone defines the term, the idea behind the issue is plagiarism. So to be on the safe side in search-terms and offer quality to readers, it would be best to write and use original content whether within your website or for off page marketing.