Okay kiddo, have you ever noticed a web link that has weird words at the end like "utm_source" or "utm_campaign"? Those are called UTM parameters.
Now, imagine you have a lemonade stand and you want to know how many people are coming to buy lemonade from different places like Facebook or Instagram. When you put up a sign that says "Buy one get one free lemonade on Facebook", you can add a UTM parameter like "utm_source=facebook" to the end of the web link.
When someone clicks on that link on Facebook and comes to your lemonade stand, you'll know the source was Facebook because the UTM parameter told you so!
UTM parameters help people who own websites to track where their visitors came from, which links people clicked on, and what advertising campaigns worked best. It's like a secret code at the end of a web link that tells the website owner about their visitors.