What is duplicate content?

In a nutshell, duplicate content is identical, or “appreciably similar”, content that appears on the Internet in more than one unique website URL.

If you have the same content on more than one page on your website or multiple websites you control, you have duplicate content.

While not susceptible to a Google manual penalty, duplicate content can hurt search engine rankings because it can be difficult for search engines to decide which version is more relevant to a given search query, thus reducing the chances that either version ranks well.

In terms of authority, link equity can be diluted because other websites must choose between the duplicates as well. Instead of all inbound links pointing to one URL, they link to multiple URLs, spreading the link equity among the duplicates. This dilutes link equity which should be concentrated on one URL reducing the authority of the page and its ability to rank well.

Additional information:

https://developers.google.com/search/docs/advanced/guidelines/duplicate-content