Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Mostly, this is not deceptive in origin. Examples of non-malicious duplicate content could include:

• Discussion forums that can generate both regular and stripped-down pages targeted at mobile devices
• Store items shown or linked via multiple distinct URLs
• Printer-only versions of web pages

If your site contains multiple pages with largely identical content, there are a number of ways you can indicate your preferred URL to Google. (This is called “canonicalization”.) More information about canonicalization.

However, in some cases, content is deliberately duplicated across domains in an attempt to manipulate search engine rankings or win more traffic. Deceptive practices like this can result in a poor user experience, when a visitor sees substantially the same content repeated within a set of search results.

Google tries hard to index and show pages with distinct information. This filtering means, for instance, that if your site has a “regular” and “printer” version of each article, and neither of these is blocked with a noindex meta tag, we’ll choose one of them to list. In the rare cases in which Google perceives that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we’ll also make appropriate adjustments in the indexing and ranking of the sites involved. As a result, the ranking of the site may suffer, or the site might be removed entirely from the Google index, in which case it will no longer appear in search results.

There are some steps you can take to proactively address duplicate content issues, and ensure that visitors see the content you want them to.

Source: Duplicate content – Search Console Help