A canonical link is a tag in the page header by which a website indicates which address is the preferred version of the given content. It is used for duplicates arising from parameters in the address, filters, print versions, or products available in multiple categories. It is recommended that every page contain a canonical link to itself, which prevents unwanted duplicates from parametric addresses. It is important to know that this is a recommendation, not a command – a search engine may ignore it if it finds that the content of the pages is different, or if it contradicts other signals. The most common mistake is a canonical link pointing to the homepage or to a non-existent address, which can remove entire sections of a website from the index.
See also: Duplicate content, Canonical domain version, URL parameters.
