Canonical Tag.

A canonical tag is a piece of HTML that tells search engines which URL a website prefers when the same or very similar content can be accessed through several URLs. It is added inside the head section of a page using rel="canonical" and points to the preferred version of the URL. For example, a product page might be available at example.com/shoes and example.com/shoes?source=instagram. If both URLs show the same product, the canonical tag can point to example.com/shoes as the preferred version. Canonical tags are also useful when pages are accessible with different tracking parameters, sorting options, capitalisation, trailing slashes or alternative URL paths. The canonical URL should normally be the complete preferred address, including HTTPS and the correct domain. An indexable page can also contain a self-referencing canonical tag that points to its own URL. A canonical tag is a strong signal, not an absolute instruction. Google may choose a different canonical URL if the page content, redirects, internal links, sitemap or other signals suggest that another URL is more appropriate. Canonical tags should only connect duplicate or substantially similar pages. They should not be used to force unrelated pages to compete as one page, hide low-quality content or replace a proper redirect when an old URL has permanently moved.

Canonical tags help search engines understand which version of a duplicated page should be treated as the main URL. This can help consolidate signals associated with duplicate URLs, keep search reporting focused on the preferred page and reduce unnecessary crawling of repeated versions. Without clear canonical signals, Google may select a different URL from the one the website owner expects. This can result in an unwanted parameter URL, outdated path or alternate version appearing in search results. Canonical tags work best when they agree with other signals. Internal links, XML sitemaps, redirects and canonical tags should consistently reference the same preferred URL.