Google's 2015 complete presentation on duplicate content and how Google handles it.
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."
Matt Cutts answers a question about duplicate content in 2013.
While duplicate content is not technically a Google penalty, it can still sometimes impact search engine results.
"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. If your site suffers from duplicate content issues, and you don't follow the [guidelines], we do a good job of choosing a version of the content to show in our search results." Google Search Central Guidelines
No, Google wants unique original content that is relevant to the topics. It's important to understand what Google considers duplicate content. Duplicate content can happen naturally, Ex. Having a new slightly updated terms of service, but this wouldn't be categorized as abusive, deceptive, or malicious or manipulative content. This example is perfectly fine and nothing to worry about. Something that Google would consider as spam is an RSS auto blog to a blog site.
No, duplicate content is not mentioned once in Google's Search Quality Raters Guidelines.
No, there is no duplicate content penalty applied by Google, however, Google's algorithm will rank the most relevant and popular version of the content (sometimes even if it's not from the original author).
Technically, it's copied content, but for Google that’s not really an issue because these are things that people are not searching for. People are looking for your primary content.
No, Google's algorithm does not currently look for the owner of the original content. Google is more focused on including the content with relevant topics.
Google wants to show the most relevant content and original does not necessary mean it's the most relevant. Watch this clip from Google Office hours answering questions about duplicate content to learn more.
Google recommended to create original and relevant content for each page. If you have two pages that are similar, you can merge the content (if there is no business reason to have two similar or duplicate pages) and create a 301 redirect from the old URL to the main URL.
Another method is using canonical link elements, however, these can sometimes be ignored by Google. A canonical tag is HTML code that tells search engines what page is the master copy for duplicate, near-duplicate and similar pages. It is the most common method used to tell search engines that a specific URL represents the master or original copy of a page. Use can use this method to quickly fix duplicate pages or if you ever republish a blog post that first appeared elsewhere.
No, it's not considered duplicate content.
Check Google Search Console for duplicate titles and descriptions or use crawler tools. You can also you tools like Copyscape or plagiarism checkers, or do a Google search using “quotes.”