[sociallocker]A canonical tag is a meta tag in the head section of the HTML of a webpage that specifies to search engines that a specific URL represents the preferred version of a page. Using the canonical tag avoids problems with duplicated content used on multiple URLs of your website. The canonical tag prevents issues with duplicated content by telling to search engines the URL of the page that you want to be displayed in SERPs.
How does the canonical tag work?
The canonical tag need to be added in the head section of the HTML of every page that is a duplicate of another page on your website to avoid ranking penalisation on SERPs.
If you look for restaurants in Milano Centrale starting from the main page of Just Eat Italy you get redirected to this URL (hereinafter “Original URL”):
The page shows all the restaurants listed on Just Eat that are available to deliver food at Milano Centrale. If you look into the HTML of the page you will find inside the head section this meta tag:
<link rel="canonical" href="https://www.justeat.it/area/20124-milano">
This above is an example of a canonical URL tag. This one in particular tells to search engines that the content in the page at the Original URL is duplicated from another page. The URL of the page that can be listed on SERPs is the one at the URL inside the tag[/sociallocker]