The Canonical tag is an HTML element that informs search engines which version of a page should be considered the "authoritative" or "primary" version. It is used to prevent duplicate content and ensure that search engines index the preferred version of a page.
Duplicate content can cause confusion for search engines and might lead to the wrong page being displayed in search results. By using a Canonical tag, webmasters can control which version of a page is prioritized for indexing and ranking.