What is the difference with None (direct)?
This is talking about the HTTP Request Header, Referer, Referer - HTTP | MDN
"The Referer header allows a server to identify referring pages that people are visiting from or where requested resources are being used.
When you click a link, the Referer contains the address of the page that includes the link. When you make resource requests to another domain, the Referer contains the address of the page that uses the requested resource. "
None (direct) means there was no Referer header. Some browsers do not use the referer header due to privacy concerns, and some extensions will cause it to not be sent as well. Another large potential source of traffic showing None (direct) is likely going to be Automated Traffic, Crawlers/Spiders like Google’s, Monitoring Services, among others.