Imagine your website has a product page with two different URLs: example.com/product and example.com/product?ref=homepage. Both show the exact same content, but search engines might treat them as separate pages. A canonical tag solves this by telling search engines, "Hey, this is the real URL — focus on this one."
When your site has duplicate or very similar content across multiple URLs, search engines get confused about which page to display in results. The canonical tag eliminates this confusion by pointing to the preferred URL. This is critical for SEO — it consolidates ranking power to one URL, prevents unnecessary pages from being indexed, and keeps all your traffic data clean in one place. One important note: don't put canonical tags on every page. Only use them when you actually have duplicate content issues. And always double-check you're pointing to the right URL — a wrong canonical tag can make search engines index the wrong page entirely.