It refers to having the exact same information appear in two or more websites at the same time.

According to Google, “Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar.”

Having duplicate does not automatically earn a penalty, but it can affect a site’s rankings.

Search engines tend to dislike duplicate content since it presents a lot of challenges:
• Determining which version of the content to include or keep out of their indexes.
• Determining how to allocate link metrics.
• Determining which version should be ranked in SERPs.

When is duplicate content bad?

When someone purposely takes, copy, and slightly alter content to manipulate search engine rankings. Google calls this “copied content.” This is the type of practice that might trigger penalties.

From Google: “Duplicate content on a site is not grounds for action on that site unless it appears that the intent of the duplicate content is to be deceptive and manipulate search engine results”

Depending on your actions, you can have duplicate content on a site without it being considered as “deceptive in origin.”

How to prevent issues with duplicate content?

There are a few practices that can help you fix or prevent duplicate content issues:
• Setting up a 301 redirect from the duplicate content page to where the original content is hosted.
• Using the rel=canonical attribute, which instructs search engines to treat a page as a copy of a specified URL.
• Using meta robots with the values “noindex, follow” in the HTML head to de-index a duplicate content page.
• Configuring a preferred domain and specify robot parameter crawling in Google Search Console.