A canonical tag is a link element that is placed within the header section of a webpage. The tag is used either when a URL features different query string parameters or when the content of a URL is replicated and repeated on other internal pages.
The canonical tag is used to prevent search engines from treating different versions of the same repeated webpage as unique. The canonical tag is therefore used to inform search engines that anything with that tag should be considered the only source of that particular content that should be included in the search engine’s results pages.
