About UTM Codes
UTM codes is meta data coded in a URL so that your Analytics software (typically Google Analytics) can attribute the source of the traffic properly. Good examples of this are email and Post Cards. Without a UTM code - when a person clicks on a link in an email it is attributed in the traffic channel 'Direct Traffic' (see 
Traffic Channels Explained ).
What is a UTM code?
https://company.com/?utm_source=mailchimp&utm_medium=email&utm_campaign=welcome
The UTM code in the example above is this part:
?utm_source=mailchimp&utm_medium=email&utm_campaign=welcome
A Valid UTM codes must contain these parts:
- utm_source - this is where the traffic came from: Mailchimp, ConstantContact, Facebook, postal
- utm_medium - the medium (or method) the links were sent: email, postcard (or physical), cpc (Items in medium are always lower case)
- utm_campaign - a name of the current effort. This could be as simple as 'newsletter' or more specific and even date stamped: newsletter-20230911
How do I create a UTM code?
It's easy, just determine the values for utm_source, utm_medium, and utm_campaign
Typically utm_source and utm_medium are already defined and it is the name of the campaign where you put thought into how you want to measure it.
UTM Code Examples:
Email sent from Constant Contact with a link to a product in the shopping cart:
https://company.com/shop/productid?utm_source=constantcontact&utm_medium=email&utm_campaign=buynow
UTM Code in Facebook
https://company.com/?utm_source=facebook&utm_medium=cpc&utm_campaign=fallsale
UTM Code in abandoned cart email native to WooCommerce:
https://company.com/cart?utm_source=woocomm&utm_medium=email&utm_campaign=abandonedcart
FAQs
Can I use different source names?
Yes - the source name is for you to know where the email came from and abbreviations are fine
Can I use spaces in UTM codes?
No, we do not recommend the use of spaces in UTM codes. Rather us the hyphen or underscore. Also do not use single quotes nor double-quotes
Why do I have to use UTM codes in Facebook Ads?
Without a UTM code in your Facebook advertising, your analytics will confuse the traffic you get from social media posts with the traffic from Facebook paid ads. The only way to differentiate them is with UTM codes in the links used on the Facebook ads.
References:
UTM Code Generators: