UTM codes are bits of text you can add to a link that tell Google Analytics more information about each link. Here’s a sample of what one looks like:
A well-constructed UTM will answer these questions:
Where is the traffic coming from?
How is it getting to me?
Why is it coming to me?
You can use Google's URL builder to create and track these UTMs: https://support.google.com/analytics/
Build better links to get more Google love for your links. And more traffic to your website!