Often called “FTP” but really a different thing.
There are multiple users. Each user has access only to their folders. I don’t know if there is an admin user that can see all.
There are instances for content and for suppmements. Both for QA and PROD. I don;t know if there are more.
Distribution also uses SFTP. Edify uploads metadata or content to the SFTP of distribution partners. The site admin can specify who these are.