A canonical tag is represented as rel=”canonical’ in HTML and it is a way of telling to search engines that a specific web page URL represents an authenticity of to given web page. you can find this from online, but let me explain you in my way, A canonical tag is a small piece of code embedded into a web page that can help search engines deal with multiple versions of the same page. It helps to avoid the duplicate content issues. which means, if you have many URLs with the similar content, then it will be affect your website ranking in SERP positions. So, the canonical tag is help us to avoid the duplicate content issues.