Demand and conversion
Tags appended to a link so that analytics can tell where a visit came from — useful exactly to the degree that the naming is disciplined.
Formula
?utm_source=…&utm_medium=…&utm_campaign=…&utm_content=…&utm_term=…
- source
- the property the click came from: newsletter, instagram, partner-name
- medium
- the class of traffic: cpc, email, social, referral — a short controlled list
- campaign
- the initiative, named to a written convention
- content
- which creative or placement, for A/B separation
- term
- the keyword, for paid search
UTMs are free and self-inflicted. The entire value depends on a convention written down once and applied without exception, because analytics tools treat Facebook, facebook and FaceBook as three sources and will never tell you they are the same thing.
Never put personal data in them. They travel in the URL, are logged by every intermediary, appear in referrer headers and get shared by users — which makes an email address in a UTM a data-protection incident rather than a tracking convenience.
A UTM on a link between two pages of your own site starts a new session and re-attributes the visitor to the internal campaign, destroying the original source. It is the fastest way to make organic traffic disappear into a channel that produced none of it.
The definitions are the easy part. Whether the figure on your dashboard was computed this way is a different question, and usually the more expensive one.