There are only 3 default medium in Google Analytics i.e Organic, Referral and None.
Google Analytics detects three mediums without any customization.
- The first default medium is “organic.” It represents traffic that comes from organic, or unpaid, search results.
- Another default medium is “referral.” Any traffic that comes to your site from another website that’s not a search engine will show up in your reports as a “referral.”
- The final default medium is “(none).” This medium is applied only for users that come directly to your site by either typing your URL into a browser or clicking on a bookmark. In your reports, you will see these users have a source of “direct” and a medium of “(none).”
Learn more here: https://support.google.com/analytics/answer/6099206