# Traffic sources

Category: [Analytics & Measurement](https://seo-geo-glossary.com/en/glossary/category/analytics-measurement/) › [Traffic sources](https://seo-geo-glossary.com/en/glossary/category/analytics-measurement/traffic-sources/)

**Traffic sources** describe where the visits to a website come from, for example search engines, other websites, social networks or direct entry. Analytics tools assign each session to a source, a medium and a channel.

## Source, medium and channel in GA4

- **Source:** the specific origin, such as `google` or a domain name
- **Medium:** the type of origin, such as `organic`, `referral` or `cpc`
- **Channel:** a group of sources and mediums, defined by rules in the default channel group

Google's help page lists rules for several channels:

- **Direct:** source is `(direct)` and medium is `(not set)` or `(none)`
- **Organic Search:** source is on a list of search sites, or medium is `organic`; per its description, this includes Google's AI Overviews and AI Mode
- **Referral:** medium is `referral`, `app` or `link`
- **AI Assistant:** medium is `ai-assistant`, or the referrer is on a list of AI assistants
- **Unassigned:** no channel rule matches

The default channel group contains further channels, including Paid Search, Organic Social, Paid Social, Email, Display, Affiliates, SMS and Audio. The full list of rules is in Google's help page.

GA4 also reports sources at different scopes. First-user dimensions show how a user arrived the first time, session dimensions show the source of each session, and event-scoped dimensions apply the selected attribution model.

Campaign links can carry tracking parameters such as UTM parameters, so that paid and email visits do not fall into Direct or Referral.

## Example

A row `google / organic` belongs to Organic Search. A row `trade-magazine.example / referral` belongs to Referral. (Invented example.)

## Related terms

- [Direct traffic](https://seo-geo-glossary.com/en/glossary/direct-traffic/index.md)
- [Referral traffic](https://seo-geo-glossary.com/en/glossary/referral-traffic/index.md)
- [Dark traffic](https://seo-geo-glossary.com/en/glossary/dark-traffic/index.md)
- [AI referral traffic](https://seo-geo-glossary.com/en/glossary/ai-referral-traffic/index.md)
- [Organic traffic](https://seo-geo-glossary.com/en/glossary/organic-traffic/index.md)
- [Google Analytics 4 (GA4)](https://seo-geo-glossary.com/en/glossary/google-analytics-4/index.md)
- [UTM parameters](https://seo-geo-glossary.com/en/glossary/utm-parameters/index.md)

## Sources

- [[GA4] Default channel group – Analytics Help](https://support.google.com/analytics/answer/9756891?hl=en)
- [[GA4] Traffic source dimensions – Analytics Help](https://support.google.com/analytics/answer/11080067?hl=en)
- [What is a Traffic Source? – CoSchedule (secondary)](https://coschedule.com/marketing-terms-definitions/traffic-source)

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Last updated: October 7, 2026
URL: https://seo-geo-glossary.com/en/glossary/traffic-sources/