Glossary
UTM parameters
Tags added to a URL's query string that name where a link was published, so analytics can tell one placement from another.
There are five, and they are a naming convention rather than a standard: utm_source names where the link was published, utm_medium names how it travelled, utm_campaign groups the placements together, and utm_term and utm_content are optional detail. Analytics tools read them because everyone agreed to, not because a specification says they must.
They exist because the alternative does not work. The referrer header is missing on most clicks, so a tool relying on it reports a large share of traffic as coming from nowhere. UTM parameters travel in the URL itself, where no privacy setting strips them and where they survive being pasted into a chat window.
The common mistakes are inconsistency and over-tagging. "Newsletter", "newsletter" and "Email newsletter" are three sources to a tool that compares strings, and a tag left empty is worse than absent because it reports a blank placement. Pick a convention and apply it before publishing, because a link cannot be retagged after it is out in the world.
