Link rel=canonical is a HTML attribute used to specify the preferred version of a webpage when multiple versions of the same content exist. It serves as a signal to search engines that the specified URL is the authoritative source for the content, helping to avoid duplicate content issues and improve search engine rankings. Essentially, it acts as a “master” link, directing search engines to the original and most relevant version of the webpage. This allows for better organization and indexing of web content, ultimately providing a more seamless and accurate browsing experience for users.