UTM parameters are standardized query-string tags — utm_source, utm_medium, utm_campaign, and optionally utm_term and utm_content — appended to a URL to identify the specific traffic source, marketing channel, and campaign that drove a click.
Originally popularized by Google Analytics (UTM stands for Urchin Tracking Module, after the company Google acquired to build it), the format is now a de facto standard read by most analytics platforms. Because UTM tags are entirely visible in the URL and set manually by whoever builds the link, they're only as accurate as the person tagging them — inconsistent naming is a common cause of fragmented campaign reports.
A link shared in an email might read example.com/?utm_source=newsletter&utm_medium=email&utm_campaign=spring_sale, telling the analytics tool the visit came from the newsletter source, email medium, and spring_sale campaign.
Only utm_source, utm_medium, and utm_campaign are generally necessary to identify a traffic source and campaign; utm_term and utm_content are optional and mainly used for keyword or ad-variation tracking.
No, but inconsistently tagged URLs can create duplicate-content issues if search engines index them separately, which is usually avoided with a canonical tag pointing to the clean, untagged URL.
Inconsistent capitalization or naming (like 'Email' vs 'email') creates separate entries in reports instead of one combined line, fragmenting the data — most teams maintain a naming convention to prevent this.