Duplicate Content refers to when a piece of web content is copied on multiple URLs.
This can occur on the same domain as the original piece of content or on another domain.
Duplicate Content is penalized by search engines as it is viewed as being dishonest & a workaround hack for sites that do not want to take the time to build out their own content properly.
Why Is Duplicate Website Content Bad?
Lazy webmasters used to copy content from other websites that was performing well & place it onto their website in order to save time.
Search Engines became keen to this & began to penalize the sites that they noticed were copying the other sites in order to discourage this poor behavior.
While this does not always happen, it is how search engines are designed.
It can be especially frustrating when a group of Amazon sellers steal content copy & all place it on their products, as that has caused clients de-indexation issues before.
In terms of your own site content, you want each page to be unique & to add value to the user’s experience & repeating your content (without proper directives) does not add value & also can lead to your content cannibalizing other rankings, if not leading to indexation errors.
All content that is published to the web should be unique & add value to the end user reading it.
How To Avoid Duplicate Content Penalties
The easiest way to avoid duplicate content penalties is to not copy content from another URL & publish it to a new one.
When using the same landing page for multiple channels (i.e. organic search, paid search & sponsored social), always be sure to place no-index tags on the paid landing pages so that they do not interfere with the performance of the organic page.
When a page heavily references another page (whether the other page is on your domain or another), place a canonical tag on the new piece signaling that the old piece is the original piece of content, in order to not get potentially penalized.