In short. UTM parameters label destination URLs so Google Analytics can report campaign sources, media and campaigns through traffic-source dimensions.

Definition: UTM parameters are campaign labels added to destination URLs to identify the source, medium and campaign associated with incoming traffic. Google Analytics uses these labels to populate traffic-source reporting fields, called dimensions.

Key facts

As of 17 October 2026, Google's campaign URL builder documentation describes utm_source as the referrer and utm_medium as the marketing medium.
Google's traffic-source dimensions guide explains that parameter names and values appear as dimensions and dimension values in reports and explorations.
Google's scope documentation distinguishes First user source from Session source: the former describes initial acquisition, while the latter describes the origin of a session.
Google's Manual report documentation lists Session manual source, Session manual medium and Session manual campaign name among its reporting fields.

What does a campaign URL look like?

Google's URL builder guide provides this sample campaign URL:

https://www.example.com/?utm_source=summer-mailer&utm_medium=email&utm_campaign=summer-sale

The question mark introduces the parameters, each equals sign joins a name to its value, and ampersands separate the pairs. In this example, summer-mailer identifies the source, email identifies the medium and summer-sale identifies the campaign.

The same guide defines these labels:

Parameter	Meaning
`utm_source`	The referrer.
`utm_medium`	The marketing medium.
`utm_campaign`	The product, slogan or promotional code.
`utm_term`	The paid keyword.
`utm_content`	A label that distinguishes creatives, such as separate links within an email.

How do labels become analytics dimensions?

A dimension is a reporting field; a dimension value is an entry in that field. Google's traffic-source guide explains that manual tagging adds UTM parameters to destination URLs and makes their values available in reports, explorations, audience builders and segment builders. Thus a label such as email becomes a value used to group traffic.

The report's scope determines which acquisition relationship a field describes. Google's scope guide describes a session as a period of interaction with a website or app. First user dimensions describe how a user initially arrives, and their values remain the same when that user returns. Session dimensions describe the origins of sessions for new and returning users.

The same guide also distinguishes event-scoped dimensions, which assign credit for key events: interactions marked as important to the business. Choosing a reporting field therefore includes choosing its scope.

Where are manually tagged campaigns checked?

Google's Manual report guide gives this route: Reports, then Life cycle, then Acquisition > Overview. The Sessions by Session manual source card contains View Manual campaigns.

The report includes Session manual campaign name and Session manual ad content alongside source and medium. These fields describe campaign information associated with the start of a session. The report requires successful delivery of UTM parameters in the website's click URL. Comparing those fields with the intended link labels provides a check on campaign tagging.

FAQ

Does capitalization matter?

Yes. Google's URL builder documentation treats parameter values as case sensitive. Use consistent capitalization when assigning campaign labels.

Why do First user source and Session source differ?

They describe different acquisition relationships. Google's scope documentation explains that First user values persist when you return, while Session dimensions describe the origins of new sessions.

Sources

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