There is only 3 default mediums 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).”