Direct Answer
UTM tracking uses query parameters (utm_source, utm_medium, utm_campaign, utm_content, utm_term) appended to URLs to tell analytics tools where a click came from. UTMs are the spine of attribution — without them, GA4 can't tell you which campaign produced which lead.
Voice answer (≤30 words)
“UTM tracking uses query parameters on URLs to tell analytics where a click came from. It is the foundation of attribution.”
Standardize: lowercase, hyphen-separated, no spaces. utm_source=google not utm_source=Google.
Inside an organization, also tag internal cross-links so AI-cited deep links carry attribution into GA4.
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