When we create a website, it may happens that two or more pages have the same structure, content and their is slight difference. So in such cases, when search engines crawl the website and find these pages, it flags them as duplicate content which ultimately hampers the website traffic. Hence, to make certain that this issue won’t happen, there is a meta tag called canonical tag, you can define in the page code that basically tells the search engine that the URL present in the canonical tag is the original URL and the search engine should consider indexing the canonical URL instead of the current page URL in which the search engine crawler is present.