Duplicate content is a common issue. There are many ways content can get duplicated:

1. The content of a web page is available in different formats: web page, printable page, PDF, mobile phone page, etc.

2. The content of a web page is syndicated, for example news articles or blog posts.

3. The content management system (CMS) displays the same content in different locations. For example, an item might be listed in a "Size" category and in a "Color" category.

4. The website owner offers mirrors to make sure that a website does not slow down when many people want to access the same page at the same time.

5. Someone stole the contents of a web page to reproduce it on other websites.