Duplicate Content
Identical or very similar content available under several URLs, which makes it harder for search engines to choose what to index and rank.
Also known as: Duplicate Pages, Copied Content
Duplicate content describes content that is almost identical across several URLs. This happens internally through URL variants, parameters, print views or filter pages, or externally when other sites copy texts. Search engines have to decide which version to index and rank, and that often weakens the visibility of all pages involved.
How duplicate content arises
Typical sources include URLs with and without a trailing slash, http and https variants, www and non-www, sorting or filter parameters, session IDs and print versions. Syndication of text on partner sites or automatic adoption of product descriptions from manufacturer catalogues also create duplicates. In an international setup duplicates appear when the same language is served from multiple domains.
How to handle it
Technical tools include canonical tags, 301 redirects, hreflang annotations, parameter handling in Search Console and a consistent URL structure. On the content side, original texts with clear added value help. When syndicating content, mark the main source as canonical. When using manufacturer product descriptions, extend, rewrite and enrich them with your own content.
In day to day online marketing
In practice duplicate content often appears unnoticed, for example through a new campaign domain, through subdomains for microsites or through identical landing pages for different ad networks. A regular audit of the most important pages prevents duplication. For campaign landing pages it is worth asking whether the page should be indexed at all: often a noindex tag is the simpler solution.