Duplicate content refers to blocks of content that are identical or very similar across different URLs, either within the same website or across multiple domains. Search engines like Google may view duplicate content as problematic because it can degrade the user experience and give the impression of manipulative or spammy practices. Duplicate content can occur unintentionally due to technical issues, print versions, incorrect URL structures, or content syndication. To avoid SEO penalties, duplicate content should be managed with canonical tags or proper redirects.