The term "Unix User" in Virtualmin is no longer appropriate, and may be confusing to new users. It should be renamed to something non-OS-specific, such as "Virtual Server Owner" or "Domain Administrator".
Since Virtualmin now works (or soon will) on other OS platforms besides Unix, OS-specific terms such as "Unix User" and "Unix Group" should be renamed. This no longer makes sense on Windows or Mac OS platforms (even though Mac OS uses Unix, most users don't think of it that way).
In addition, even on Unix/Linux, it is an ambiguous term, since all users (including e-mail and FTP users) are Unix users by default. Or, the "Unix user" may not be a Unix user at all if the system is set up for LDAP. Therefore, it would be better to specify these terms by their role, not the OS platform.