Tags you add to the end of a URL to track where your traffic is coming from.

For example, a UTM code might look like this: yoursite.com/contact?utm_source=instagram&utm_medium=social&utm_campaign=spring-promo. When someone clicks that link, your analytics tool records exactly where they came from.

It's one of the simplest ways to know which campaigns, platforms, or pieces of content are actually driving results.